AN
GINNERS
DBi
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PRESENTED
TO
THE UNIVERSITY OF TORONTO
If
Examination copies of the accompany- ing Book have just reached us from the Publishers. We have pleasure in sending- one to your address.
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BOTANY FOR BEGINNERS
BOTANY
BEGINNERS
BY
ERNEST EVANS
NATURAL SCIENCE MASTER, MECHANICS' INSTITUTE AND TECHNICAL SCHOOLS, BURNLEY
Hontion
*?
I iff
MACMILLAN AND CO., LIMITED
NEW YORK : THE MACMILLAN COMPANY 1899
All rights reserved
RICHARD CLAY AND SONS, LIMITED, LONDON AND BUNGAY.
PREFACE
IT is now generally accepted by educationists that experi- mental work is an essential part of instruction in any branch of physical or natural science. Too much importance cannot be attached to knowledge gained direct from Nature ; and it is gratifying to know that many questions now set by public examining bodies are designed to test the student's own obser- vations and experience. As an instance of this, it is worth pointing out that in the syllabus for Botany, published by the Department of Science and Art, the examiners remark : —
" The examination will be especially directed towards ascer- taining the amount and character of the practically acquired knowledge possessed by the students."
To provide students with a means of obtaining such know- ledge, this little work has been prepared in the spirit of the foregoing remarks, as a guide to beginners in the practical study of plants. The attempt is often made to study Botany without the practical examination of plants, and it has produced on the popular mind an impression that the subject is uninteresting. This is the result of the old method of teaching Botany by means of ideals or definitions ; the new method is to examine the plants from as many points of view as possible, and to draw conclusions from actual observations. Studied in this way, the subject becomes one of living interest, instead of being merely a collection of technical names and terms. It is with the idea of placing in the hands of all who are interested in the study of plants a book which shall be a guide and companion during a first course that the present volume has been prepared.
PREFACE
Though the book has been primarily designed to cover the syllabus of the Department of Science and Art, it is by no means a " cram-book " for that particular examination, and a thorough knowledge of its contents will not only lay the foundation for further work, but should enable a student to pass any elementary examination in Botany with distinction. The book should also be useful to teachers in elementary schools, in assisting them to prepare object lessons with plants for the instruction of their pupils.
Teachers are recommended to see that the students perform the experiments, and keep a complete record of the results obtained. Most of the plants necessary for the experiments can be easily obtained ; the others can be grown in the school grounds. A small collection of fruits, seeds, dried and mounted plants, should be kept in all schools.
It is hoped that the introduction into this book of a series of carefully graded experiments with simple apparatus will prove useful to many students and teachers, and will be the means of making botanical science a more popular subject in the future than it has been in the past.
Many of the illustrations have been prepared, after careful consideration, by my friend and colleague Mr. W. E. Holt, to whose skill I am much indebted. Figures 128 to 131 have been drawn by my former student, Mr. H. Wright, A.R.C.S. The figures marked S. have, by the kindness of the publishers, been placed at my disposal from Strasburger's Text Book of Botany.
The questions at the ends of the chapters will serve to test whether students have clear ideas on the subjects dealt with. Those with years indicated are from papers set at the Science and Art Department's examinations ; and T. signifies Training College questions.
In conclusion, I desire to acknowledge my indebtedness to Prof. R. A. Gregory and Mr. A. T. Simmons, B.Sc., for many valuable suggestions and much help during the preparation of the manuscript, and the passage of the work through the press.
ERNEST EVANS.
MECHANICS' INSTITUTE AND TECHNICAL SCHOOLS, BURNLEY.
CONTENTS
CHAPTER I
INTRODUCTION .......... ,
CHAPTER II
MORPHOLOGY— STUDY OF THE BODY OF A PLANT
CHAPTER III
ANATOMY — STUDY OF THE SHOOT 1 6
CHAPTER IV THE STUDY OF THE SHOOT (continued) 34
CHAPTER V
ANATOMY — STUDY OF ROOTS 51
CHAPTER VI
SECTIONS, HOW TO PREPARE AND EXAMINE THEM 6l
CHAPTER VII
THE HISTOLOGY OF THE CELL 74
CHAPTER VIII
THE HISTOLOGY OF THE TISSUES 92
CHAPTER IX
THE HISTOLOGY OF THE SHOOT AND ROOT 103
CONTENTS
CHAPTER X
PAGE THE PHYSIOLOGY OF NUTRITION Il6
CHAPTER XI
THE ABSORPTION AND MOVEMENT OF WATER IN THE PLANT 137
CHAPTER XII
THE PHYSIOLOGY OF GROWTH AND MOVEMENT 152
CHAPTER XIII
TLOWER AND INFLORESCENCES 164
CHAPTER XIV
THE TERMS USED IN DESCRIBING THE FLOWER 178
CHAPTER XV
THE DEVELOPMENT AND MORPHOLOGY OF THE FLOWER . .
CHAPTER XVI
POLLINATION AND FERTILISATION .
CHAPTER XVII
THE MORPHOLOGY OF SEED AND FRUITS, AND THEIR DISTRI- BUTION 222
CHAPTER XVIII
THE PHYSIOLOGY OF REPRODUCTION " . V . .' . . 237
CHAPTER XIX
THE CLASSIFICATION OF PLANTS . . 242 I
CHAPTER XX
CLASSIFICATION OF PLANTS (contimied} 265 j
CHAPTER XXI
PLANT DESCRIPTION ".''.. .."".' .' .' . V . . 283:
INDEX . ........ 287;))
BOTANY FOR BEGINNERS
CHAPTER I
INTRODUCTION
Definition. — The branch of science the object of which is the study of the plant, from- as many different points of view as possible, is termed Botany. All its laws can be proved by observation and experiment, and it is consequently known as one of the concrete sciences. If we wish to include all plants it is impossible to clearly define what is meant by a plant, because the higher plants differ in many respects from the lower, and so many exceptions to any rule we may state present themselves. It is true that in olden times our forefathers divided all forms of life into animals and plants, but we find we cannot, with the knowledge of to-day, draw a clear boundary line between them. It is easy to recognise the difference between an oak tree and a horse, but when the lower forms of life are examined no clear division can be drawn between animals and plants. All living things are built up of the same kind of material, vfz. — protoplasm. Protoplasm has been called the physical basis of life, because life is never found apart from it. There appears to be no difference between the protoplasm obtained from animals and that obtained from plants. In fact, what we speak of as the tree of life is forked, the animals being found on one side and the plants on the other, .-IB B
BOTANY FOR BEGINNERS CHAP.
and both of them spring from the lowly forms which are found at the base.
Higher Animals. Higher Plants.
E.g. Horse. E.g. Oak.
Lower forms of life.
Living and Non-living Bodies.— It will be well to at once consider the question of the differences between living and non-living bodies ; and here a fairly clear boundary line can be drawn.
1. Living bodies are characterised by the nature of their external form. Their shape is definite, and bounded more or less by curved surfaces. Non-living bodies are either amorphous, that is without shape ; or crystalline, that is bodies with a definite shape. Crystals are bounded by flat surfaces meeting in sharp edges.
2. Living bodies are able to reproduce their kind, but non- living bodies have not this power of reproduction.
3. Living bodies take in food, which supplies material for growth, the growth taking place from the inside. Non-living bodies cannot take in food, but tjiey can increase in size if placed under suitable conditions. The growth or increase in size of a crystal always takes place on the outside, not internally like the growth of either animals or plants.
The Object of the Plant.— Plants, then, are living things, and we must learn to treat them as such. Plants produce seeds, but not, as the reason is sometimes stated, for the use of man, but so that the continuity of the particular race of plants can be kept up. The living, working, struggling plant, has only
INTRODUCTION
one object in life, that is, to reproduce its kind. All the parts of the plant are designed with this object in view ; the shape, colour, and perfume of the flowers, and all the various contriv-
FIG. i. — Illustration of the difference in the external forms of the mineral, vegetable, and animal kingdoms.
ances with which plants are endowed, are to be regarded as means towards accomplishing this reproduction.
Scope of Our Lessons. — We shall have to consider the plant from the following points of view : — (i) Morphology, or the science of form and structure ; (ii) Physiology, or the science of function j (iii) Classification, or the science of relationship.
B 2
.BOTANY FOR BEGINNERS CHAP.
Morphology. — That portion of the study of living things which deals with the shape and structure of the various organs of plants or animals is termed morphology. Morphology is divided into anatomy, which means, as far as our lessons are concerned, the structure of the plant to the extent it can be made out by the aid of a knife, the naked eye, or by the aid of a simple lens ; and histology, or the minute structure of the various organs which require the use of the compound micro- scope for their complete study.
Physiology. — This division of botany is concerned with those functions which, taken together, constitute the life of the plant. Just as morphology is concerned with what plants are, so "physiology deals with what they do. There are several divisions into which physiology can be divided, for example : —
1. The Physiology of Nutrition, or how a plant obtains its food, together with the changes that go on in the food due to the activity of the living substance of the plant, so that the food may become part of it, or become converted into sugar, starch, cellulose, and proteids.
2. The Physiology of Movement, or how plants move. That various parts of plants can move is shown by the opening and closing of flowers, the so-called sleep of leaves, and the changes in the position of stems, such as the twining stems of the hop, and the tendrils of the vine. This department of physiology tries to answer all questions relating to the causes that produce the various movements of plants, and how these movements are affected by the action of light, heat, and moisture.
3. The Physiology of Reproduction, or how plants reproduce " their kind. Some plants reproduce by means of bulbs and
tubers. This kind of reproduction is termed vegetative, because the parts of the plant that enter into the process are only portions produced by the vegetative functions of the plant. In far the greater number of cases, plants reproduce their kind by means of seeds. This kind of reproduction is termed 7 sexual.
Classification. — The province of classification is to point out the relationship between different plants. Many methods of classification have been devised, and many of them are known as artificial systems.
One of the best known is that of Linnaeus, which is based on
INTRODUCTION
the number and arrangement of the parts of the flower. All the various artificial systems have been superseded by that called the Natural System, which is based on the resem- blances and differences of plants. The natural system ot classifying plants is the most perfect yet used, though it is not up to the present complete, because the relationships between different plants have not been fully worked out.
To make the above divisions of our subject yet more clear to the reader we arrange them in a tabular form, which should be carefully learnt.
Botany.
I J
Morphology. Classification. Physiology.
I I
Anatomy. Histology.
Nutrition. Movement. Reproduction.
Life-History of a Plant.— Every plant possesses what is termed a life-history, that is, its life has a beginning, it passes through certain stages, old age comes on, and at last it dies. All the changes that a plant undergoes from birth to death make up its life-history. In all the higher plants the life-history com- mences with the germination of the seed, continues as that of the seedling, is prolonged as the plant becomes mature, then flowering takes place, seeds are produced, the parent dies, and the continuity of the race is kept up by the young plant in the seed.
Necessity for Practical Work.— Having now given some idea of the scope and aims of botany, and the boundary lines which mark off the different divisions of the subject, the importance of practical work must next be insisted on.
No true knowledge of natural history can be obtained without practical work ; and there is no doubt that such work is well adapted for cultivating the powers of observation and attention to details, attainments which are likely to prove of value in whatever walk of life the student may afterward find himself.
Botany is one of the best subjects with which to commence the study of science, because the necessary materials for
BOTANY FOR BEGINNERS
CHAP.
practical work are abundant, and the instruments required in the early stages are very simple.
Full instructions will be found for carrying out the experiments given in the following pages, and if the student will only per- form them, and carefully make notes of the results obtained, he will, after working through the book, have a good working acquaintance with elementary botany.
SUMMARY.
Botany concerns itself with the study of plants. It is a concrete science.
Boundary lines can be easily drawn between the higher plants and the higher animals, but the line of demarcation is difficult to define when the lower forms of life are under consideration.
Plants and animals are built up of protoplasm. The tree of life is a forked one.
DIFFERENCE BETWEEN LIVING AND NON-LIVING BODIES.
Living.
1. Their shape is definite.
2. Can reproduce their kind.
3. Can take in food and grow internally.
Non-Living.
1. Either of no definite shape or crystalline.
2. Cannot reproduce their kind.
3. Cannot take in food and can only grow from the outside.
The one object of the plant is to reproduce its kind.
Morphology
is
the science of shape and structure. It is divided into —
Anatomy or struc- ture made out with- out the use of the com- pound microscope.
Histology or struc- ture made out by the use of a compound microscope.
SCOPE OF THE SUBJECT.
Physiology
is
j the science of func- I tion, or what a plant can do. It is divided into —
Physiology of nutri- tion.
Physiology of move- ment.
Physiology of re- production.
Classification.
is
the science of rela- tionship.
Embracing plant description, and plac- ing the plant in its true position in the natural system.
INTRODUCTION
QUESTIONS ON CHAPTER I
(1) Define the term botany. What are the objects of botany?
(2) What is meant by a concrete science? Why is botany placed among the concrete sciences ?
(3) Can a clear boundary line be drawn between the higher animals and the higher plants ? If so, why ?
(4) Into what divisions can botany be divided ? Why is botany divided into the divisions you mention ?
(5) Give a short account of the natural system of classification.
(6) What is meant by the life-history of a plant ?
(7) Why is practical work of such great importance in natural history ?
CHAPTER II
MORPHOLOGY.— STUDY OF THE BODY OF A PLANT
Parts of a Plant. — If any ordinary plant, such as a wall- flower or mustard plant, be examined, we find that it consists of certain well defined parts.
These parts are known as root and shoot ; the shoot can again be divided into stem and leaf.
The root and stem are continuous, and together form the axis of the plant. The root is called the descending axis, and the stem the ascending axis. By the repetition of these parts a plant is built up. From a morphological point of view, these parts of a plant are termed its members, and they can be classified under four main heads, as follows : —
1. Root-structures. — These are as a general rule found at the base of the plant. They serve to fix it to the soil, and to take in water and minerals. The root of the mustard plant may be mentioned as a typical instance.
2. Stem-structures. — These may be aerial, as in the stem of the oak, that is, those which grow upwards into the air ; or, they may be found beneath the soil, as in Solomon's Seal, when they are called subterranean stems. In some cases, like the strawberry, they creep along the surface of the ground, when they are known as creeping stems. From the stem both leaves and buds are developed as lateral outgrowths.
3. Leaf-structures. — Leaves are, as a general rule, thin, and green or brightly coloured. They are produced by the stem.
CH. II
MORPHOLOGY
4. Hair-structures.— These may grow from all .parts of the plant and may be short, or long and silky. All hair structures agree in being developed from the epidermis or skin-like coverings of the plant. Some hair-structures serve to keep off unwelcome guests, like ants ; others again, like those of the horse chestnut, secrete or form a kind of glue to protect the young buds from cold ; while some, like the dandelion, take part in scattering the seeds.
Organs.— From a physio- logical standpoint the parts of a plant are spoken of as its organs. An organ is a structure which is able to perform some special work, e.g., the root is an organ be- cause it fixes the plant to the soil.
EXPT. i.— Obtain a nearly full-grown Wallflower plant, and examine it. "Observe —
(i) The shoot is erect and branched, and the older part is hard and woody. The upper part of the shoot is green, and the lower part of it is covered with a pale- brown bark.
(ii) That the shoot can be divided into stem and leaf — the leaves being outgrowths of the stem.
(iii) That the stem branches, and the branches rise from the space between the stem and leaves. The space between the leaf and stem is called the axil of the leaf (Fig. 3).
(iv) That the leaves are green, thin, veined, and lance-shaped.
(v) The shoot is hairy, the hairs lying very close to the surface. Pass the leaf through the ringers and note what the hairs feel like.
(vi) That the main root is nearly colourless and tapers from the point where it joins the stem to its apex. Springing from the main root will be seen a very large number of secondary roots, or root branches, which help to fix the plant to the soil.
FIG. 2.— Wallflower Plant.
10
BOTANY FOR BEGINNERS
CHAP.
The stock, or any ordinary plant will do for this experiment.
The body of the wallflower is built up of the same members as are found in an oak tree (Fig. 4), a potato, or many other plants.
The Parts Present in a Seed.— Most flower- ing plants are produced from seeds, and at this point it will be well to consider the structure of seeds. The same parts can be found in a seed as have been recognised in the wallflower, along with other parts which belong to the parent plant. The Structure of a
FIG. 3. — Stem and leaf; showing axil. Bean.
EXPT. 2. — Soak a , few
Scarlet Runner beans in water for twenty-four hours, and examine one of them. Note —
(i) The bean is kidney-shaped, and along one side is a dark scar — the hilum — -where the seed was attached to its stalk.
VV '
FIG. 4.— Oak Tree.
(ii) The small hole near the hilum — the micTQpyle. It can be seen best by wiping the seed and gently squeezing it, when water will ooze out.
MORPHOLOGY
(iii) If the point of a penknife or a pin be inserted opposite to the hilum, the seed-coats can be removed. The seed-coat, or Spermoderm, consists of two layers ; the outer is known as the testa, anuthlT'Tfiner is called the tegmen.
(iv) The seed-coats surround a whitish mass, which may fall in pieces ; this is the young plant or embryo.
(v) If the embryo is examined there will be found along the side near to the micropyle a small body, called the radicle, the apex of which points towards the micropyle.
(vi) Now separate the white mass, along the middle line, into its two divisions — the se§d-leaves or cotyledons.
(vii) Between the cotyledons will be found the plumule or young stem, which is continuous with the radicle, and if you use a lens
FIG. 5.— Bean Seed. A = A side view of seed. B = Showing radicle. C = Bean, with seed coats stripped off. D = Seed coats. E = The two cotyledons. F = Plumule/
you will be able to see a number of minute leaves growing from the plumule.
(viii) It care be taken in examining the embryo, it will be noticed that the radicle, plumule, and cotyledons are all joined together to form the body of the embryo.
We can represent the relations of the parts of the bean seed as follows : —
Bean.
|
Embryo. |
Cove |
rings. |
|
Cotyledons, Plumule, Testa. |
1 Tegmen. |
Radicle,
or young root, or seed leaves, or young stem.
Structure of a Grain of Wheat.—
EXPT. 3. — Take a few grains of Indian Corn, and soak them in water for a few hours, and examine in the following way : — Cut the grain lengthwise with a sharp knife, and look at half of it with a hand lens. Observe —
(i) The covering, which is made up of several layers, only two of
12 BOTANY FOR BEGINNERS CHAP.
which correspond to the testa and tegmen of the bean. The other layers belong to the fruit, for the grain of wheat is in reality a fruit (p. 19).
(ii) The micropyle is hidden by the coverings of the fruit and cannot be seen, but at one -end of the grain a firmer portion will be found, which is the embryo, and above the embryo a softer portion, the endosperm, can be distinguished. This is reserve food material for the use of the young plant.
(iii) On the cut surface of the embryo, in contact with the endosperm, a single cotyledon will be found ; and on the outside of this an upper portion, the plumule, and a lower portion, the radicle, can be made out.
The following table will show the relation of the different parts found in the grain of Indian Corn.
Indian Corn.
I I.
Kernel. Covering.
L_ _ I
I I I " I
Embryo. Endosperm. Spermoderm. Fruit.
I I I
Radicle. Cotyledon. Plumule.
Dicotyledons and Monocotyledons.— In both the Bean and Indian Corn seeds, the embryo consists of radicle, plumule and cotyledons, but the number of cotyledons differs.
The Indian Corn has only one cotyledon, but the Bean possesses two. Those plants which possess two cotyledons are referred to as Dicotyledons, and those with only one as Monocotyledons. The Bean belongs to the former, and the Indian corn to the latter.
Germination of Seeds. — The early stages of the develop- ment of the embryo are spoken of as germination. If the seed is examined during germination, we can clearly see how the various parts which are found in the embryo act during that process.
EXPT. 4. — Obtain a few Mustard seeds, and place them on a piece of flannel stretched on a saucer. Keep the flannel damp and warm. Examine the seeds from day to day, and notice : —
(i) That they begin to sprout. This is the result of the moisture and heat. At one place a small swelling appears, which is due to the radicle pushing its way through the micropyle.
MORPHOLOGY
(ii) In a few days the radVJe will have grSwn into the primary or main root, and from it a laree numtar of secondary roots develop.
FIG. 6.— Pot of Mustard seedlings, showing cotyledonary leaves.
FIG. 7. — Pot of Mustard seedlings, showing secondary leaves.
Drainayc - -
FIG. 8. — How to pot a plant.
(iii) The plumule grows upwards towards the light and the cotyledons are green.
EXPT. 5. — Take a few of the young Mustard plants used in the last experiment and a plant pot with soil in, and with a penholder make a
BOTANY FOR BEGINNERS
CHAP.
few holes in the soil. Plant the mustard seedlings, firmly pressing the soil to the roots. Water the soil ,and place the pot on a window sill. Examine every day, and notice that ther'apex of the stem gives off new leaves, and that these new leaves are very different from the seed leaves.
EXPT. 6. — Take some of the seeds of the Indian Corn used in Experiment 3, and, as before, plant them in a box or plant pot, and notice that—
(i) The plumule is the first part to appear above the soil, and its tip is surrounded by the cotyledon.
(ii) Carefully remove a plant from the soil ; the primary root or radicle is very short, and from it are produced a very large number of adventitious roots.
FIG. 9. — A Maize seedling, showing roots and leaves.
FIG. 10. — Adventitious roots of a Grass.
Adventitious roots are those roots which are not produced in regular order. Roots are also given off from the plumule just above the cotyledon. The difference between primary, secondary, and adventitious roots is well seen in the mustard and in the Indian corn. Primary roots are always formed by the elonga- tion of the radicle ; the secondary roots grow from the radicle, in regular order ; but adventitious roots are produced from the stem, or some part of the plant other than the primary root.
MORPHOLOGY 15
SUMMARY.
Farts of a Plant. — The body of a plant is built up of root and shoot. The shoot is divided into stem and leaf. The axis of the plant is built up of the root and stem. The root is the descending axis and the stem the ascending axis.
From a morphological point of view, we speak of the various parts of a plant as members ; these members are classed as root-structures, stem-structures, leaf-structures, and hair-structures.
The members are termed organs if we treat them from a physiological standpoint. The wallflower plant is built up of the same parts as the oak tree.
Farts in a Seed. — The following tables show the parts present in the seeds of the Bean and Indian Corn.
Bean. Indian Corn.
Coverings of Fruit. Absent. Coverings of Fruit. Present.
Seed-Coats. Testa and tegmen. Seed-Coats. Testa and tegmen.
Embryo is built up of radicle, Embryo is built up of radicle,
plumule, and two cotyledons. j plumule, and one cotyledon.
Endosperm. Absent. Endosperm. Present.
Marking in seed coat the hilum. i Marking in seed coat, not seen.
Opening. Micropyle. Opening. Micropyle, not seen.
This is a Dicotyledonous plant, j This is a Monocotyledonous
because it possesses two cotyle- plant because it only possesses
dons. one cotyledon.
By the germination of the seed we mean the changes that a seed goes through during its early development.
A Primary Boot is a root which is produced by the elongation of the radicle. A secondary root is a root which is produced from the primary root. Adventitious roots are roots which are produced from any part of the plant and without any regular order.
QUESTIONS ON CHAPTER II.
(1) Define the term member. Name the members which can be found in any plant you may select.
(2) What is the use of a root ? What kinds of roots are there ? (1881.)
(3) Suppose a piece of the axis of some flowering plant were shown to you, what appearances would enable you to decide whether it was part of the root or of a stem ? (1882. )
(4} Describe the structure of a grain of wheat, and the mode of its germination. (1888.)
(5) Describe and compare the seeds of the bean and of the wheat. (1887.)
(6) From what part of a stem does a branch grow ? Illustrate your answer by a sketch.
CHAPTER III
ANATOMY — STUDY OF THE SHOOT
Shoot. — Stems and leaves are so intimately connected that it is impossible to treat of one without reference to the other. The term shoot is therefore used to include both the stem and its leaves. At the apex of the shoot there is, as a general rule, the growing point, from which the leaves and branches are pro- duced. The leaves increase in size faster than the stem, which causes them to overlap the apex, forming a bud. The structure of the tip of the shoot can be made out by the aid of a hand lens. The growing point will be found at the apex of the shoot and it is surrounded by a number of minute leaves.
EXPT. 7. — Take a twig of the Horse Chestnut, and make a longi- tudinal section so as to pass through the apex.
Examine the section by the aid of a hand lens. A series of leaves, the largest on the outside and the smallest near the centre of the bud, will be found, and protected from injury by these overlapping leaves, the growing point will be fairly easily made out.
Buds. — A bud is an undeveloped shoot, and from it leaves and branches may be produced. Buds receive different names according to the parts of the plant which may be produced from them. If a bud develops into a branch it is known as a stem- bud, if foliage leaves are formed from the bud it is called a leaf-bud ; a flower-bud is one which produces a flower.
Buds are often named after their position on the shoot. If the bud is found at the end of the shoot it is called a terminal bud ; when it grows in the axil of a leaf, an axillary bud ; if the bud springs from any other part of the shoot it is known as
CH. Ill
ANATOMY— STUDY OF THE SHOOT
an adventitious bud, but these are very rare though the ten- drils of the vine are produced from such buds.
Some buds may be latent or dormant, i.e., remain undeveloped for a long time. These may become active when the ordinary buds have been destroyed by frost or accident. Trees in spring may have their leaves destroyed by frost, but after a few weeks a new set of leaves are developed, which are formed from latent
buds. Latent buds may thus save the life of the tree. Even when in the dormant state these buds increase in size and give • T rise to balls such as are often
seen, under the bark, in the Beech, Chestnut, and Lime. Latent buds also give rise to the
FIG. ii.— Twig showing; T, Ter- minal buds ; L, Lateral buds.
Fig. 12. — Stem and leaves, showing buds in the axils of leaves.
knots which are found in timber. If the main shoot of the Oak and Beech be cut down, a dense outgrowth of branches, formed from the base of the shoot, occurs ; this is called tillering. The new outgrowth is formed from the dormant and adventitious buds. It is a very common practice for farmers in the spring to roll the wheat which is sown in winter ; this is to make it
C
i8 BOTANY FOR BEGINNERS CHAP.
tiller. In other cases they have the young growing points eaten off by sheep to produce the same result.
Those buds which persist through the winter are protected with special bud-scales, which may be membranous or scaly in their texture. The bud-scales of the Oak are dry, those of the Horse-Chestnut sticky, from the secretion which they produce.
FIG. 13.— Tillering of Stump of Elm.
In some cases bud-scales may be hairy, and in others perfectly smooth. The bud-scales as a general rule fall off as the bud opens, thus allowing the leaves to expand.
EXPT. 8.— Obtain a small branch of the Hazel, and note the position of the buds. That at the apex of the branch is the terminal bud, those behind are the lateral ones.
EXPT. 9. —Take a twig from any tree in winter, and keep it in water in a warm room. Note —
(i) It will produce leaves from the leaf-buds ; if flower buds are present, flowers may be produced.
(ii) This experiment shows that the materials necessary for the de- velopment of the leaves and flowers are stored up in the tree, and when the necessary temperature is obtained development takes place.
in ANATOMY— STUDY OF THE SHOOT 19
EXPT. 10. — Cut sections through the apex of the buds of the Horse Chestnut and Sycamore. Note —
(i) The overlapping scale leaves.
(ii) The young foliage leaves.
(iii) The apical growing point.
(iv) The arrangement of the different parts should be shown in a sketch.
Kinds of Plants. — Plants may be annual, biennial, or perennial, i.e., they may last one, two, or more years.
Annual Plants produce seeds during the first year of growth and then die. Wheat, Barley, Peas, Beans and Mignonette, are examples.
Biennial Plants are those which during the first year of growth store up reserve materials, these substances being used for the production of flowers and seeds in the second season. Thus, biennial plants must live two years. Turnip, Cabbage, Foxglove, and Beet, are typical examples.
Perennial Plants live and grow for three or more years. They may be trees or shrubs, such as the Oak, Beech, and Hawthorn ; or they may be herbs, like the Daisy, Snowdrop, Wild Hyacinth, and Primrose. The herbaceous perennials have underground stems from which the leaves and flowers are produced ; the aerial parts die down each season.
The Ascending Axis. — The ascending axis is a very important part of the plant ; though leaves may be absent, and in a few cases roots may not be developed, the stem is always present. The stem bears buds, leaves, flowers, and fruits, and connects the leaves with the roots. If the stem is produced by the elongation of the plumule, it is called primary or normal. The place on the stem from which a leaf arises is termed a node, and the space between two nodes is termed an inter- node. In some cases the nodes are thickened, as in the Stitchwort, and in a few cases adventitious roots may spring from them, as in the Ivy.
Herbaceous Stems.— The ascending axis may be soft and green, and die down at the end of the season, when it is called a herbaceous stem. Herbs are plants which fulfil their life-history in a single season ; they are also called annuals. Annuals, such as the Stock, Oats, and Indian Corn, also produce seeds at the end of their period of growth.
C 2
20 BOTANY FOR BEGINNERS CHAP.
Shrubby Stems differ from those named above in being hard and woody. They are larger than herbaceous stems ; but smaller than the stems of trees. A shrub is a dwarf tree with a number of permanent woody stems, which divide from the bottom. A shrub differs from a tree (a) in the stems being more slender, and (b) in not growing more than twenty feet high. The following are typical shrubs : — Box, Heath, Rose, Rhodo- dendron, Gooseberry and Currant.
HERBACEOUS. SHRUBBYwWOOW STEMS.
FIG. 14. — Diagram illustrating herbaceous, shrubby, and woody stems. A = Herbaceous. B = Shrubby. C = Woody. S = Section.
Woody Stems are large, and last for a number of years ; they shoV rings of growth if cut across. Our forest trees such I^LS the Oak, Beech, Fir, Lime, and Ash have woody stems. * Aerial Stems grow above the ground, as those of the Oak, Wallflower, and Foxglove. Several forms of aerial stems are distinguished : —
The Runner is a stem which creeps along the surface of the ground, and produces adventitious roots from its underside, and leaves from its upper surface, e.g., the Strawberry (Fig. 15).
The Off-set is a stem which is produced from the parent stem ; it creeps along for a short distance and then takes root, e.g., the House-leek (Fig. 16).
The Stolon is a branch which takes root at its end, thus pro- ducing a new plant, e.g.) Couch-grass (Fig. 17), Gooseberry, and Currant.
Ill
ANATOMY— STUDY OF THE SHOOT
21
The Sucker is an aerial branch given off by an underground stem ; it runs for a short distance beneath the surface, and then strikes upwards, forming a new plant, e.g.^ the Rose and Mint.
Subterranean Stems grow beneath the surface of the ground, and are often termed, in popular language, roots.
FIG. 15. — Runner of Strawberry.
FIG. 16.— The Off-set of the House-leek. FIG. 17.— The stolon of the Couch-grass.
Many perennial plants are able to exist throughout the winter by means of underground stems.
The Rhizome is a creeping underground stem which produces both roots and leaves. The roots are produced from the under- surface of the stem, and the leaves from the upper. Rhizomes
22
BOTANY FOR BEGINNERS
CHAP.
differ from roots in producing leaves and buds. Solomon's Seal and the Iris produce rhizomes (Fig. 18).
The Tuber is a swollen underground stem, and in it there is stored up large quantities of reserve materials for the production
* I c d
FIG. 18. — Rhizome of Solomon's Seal. a = bud of next year's aerial growth b = scar of this year's growth ; c, d, e, scars of previous year's aerial growth
and iu = roots.
FIG. IQ. — Part of Potato plant, with the old dark tuber in the centre. (One-third natural size.)
of a new plant. The Potato tubers are produced from the ends of stolons, and thus are formed a little distance from the parent
Ill
ANATOMY-STUDY OF THE SHOOT
plant. The so-called eyes that are found on the outside of a
potato are in reality buds, from which the next year's growth
will take place. The parent plant
dies after the production of tubers,
but not before large stores of reserve
materials have been accumulated in
the tubers for future use. If the
aerial branches of the Potato plant be
covered up with soil, their growth
will be checked and they will produce
tubers. The Jerusalem Artichoke and
the Earth-nut also produce tubers.
The Bulb is a modified stem often met with in monocotyledonous plants. It consists of a short thickened stem with a large number of crowded, over- lapping leaves. These leaves contain a large quantity of reserve material for the growth of the next season's plant. In the Onion the leaves sheathe one another, but in the Tiger Lily they only overlap. The bulb is closely allied to the tuber. The Onion, Wild Hyacinth, and Daffodil are examples of plants that produce
bulbs.
The Corm is a
very solid fleshy
stem with fewer
leaves than che bulb. In the Crocus it is a
solid, rounded, main axis, full of reserve
materials. The Snowdrop and Gladiolus
spring from corms.
EXPT. ii. — Obtain from a gardener a piece
of the runner of a Strawberry plant. Note — r IG. 21. — Corm of /-\ tr it. re
Crocus. w H°w the runner gives off roots.
(ii) How the leaves are produced. The leaves are developed from the upper surface of the
stem and from the nodes 5- the roots spring from the lower surface of the stem.
k
zk
FIG. 20. — Longitudinal section of bulb of Tulip, zk, modi- fled stem ; zs, scale leaves ; 57, terminal bud ; k, young bud ; w, roots.
24 BOTANY FOR BEGINNERS CHAP.
EXPT. 12.— Take a few plants of the Couch grass — which can be found in most meadows and in cornfields, and examine them. Select one which shows the stolon best. Note —
That the branch is given off above the level of the ground, and then bends downwards and forms a root at the end.
EXPT. 13. — If a piece of a sucker of a Raspberry plant with its attach- ment to the underground stem be obtained, the way in which it is pro- duced can be noted. It will be seen that the underground stem produces a branch, which runs for a short distance beneath the ground and then breaks through the soil and comes to the surface.
EXPT. 14. — Dig up a rhizome, either of Solomon's Seal or a Bracken Fern. To do this it is necessary to have a good trowel with which to remove the surface soil. Follow the stem so as to uncover it without breaking it, and examine. Note —
(i) The old scars produced by the leaves of previous years. These are caused by the dying down of the leaves.
(ii) The new leaves, which will break through the ground next season.
(iii) The growing point, which is protected by scale leaves.
EXPT. 15. — Take a Potato tuber and examine it. The eyes, which are buds, will be seen as small dark spots. If a young tuber be examined, the minute scale leaves round the growing point will be seen. Cut a tuber in two and notice how thick and fleshy it is.
EXPT. 1 6. — Obtain a-bulb of the Daffodil and a Crocus corm. Examine and compare them. Note —
(i) The bulb which is made up of scale leaves, many of which are thick and fleshy.
(ii) In the corm the stem is far larger than in the bulb, but the leaves are not so numerous.
Parasitic Steins. — In a few cases stems are so modified that they can fix themselves to another plant, and extract from it those materials which are necessary for their existence. Plants of this description are called parasites. The Dodder is a good example of such a plant ; it can live on the Clover, the Nettle, and the Willow. When the seeds of the Dodder germinate a long filament is formed, the free end of which moves round and round in search of a host plant — as the plant upon which it lives is called — and when a suitable plant is found it twines closely about it like a climbing plant. Suckers are produced from those parts of the filament which are in close contact with the host, and these pierce the host, and work their way inwards, to obtain food.
Ill
ANATOMY— STUDY OF THE SHOOT
25
EXPT. 17. — If a specimen of a plant can be obtained, which has been attacked by the Dodder, it should be examined. Note — (i) How the Dodder climbs round the host, (ii) How the suckers are produced.
Climbing Plants.— Plants climb over the shoulders of their weaker brethren for two reasons ; (a) because their shoots are far too weak to sup- port their own weight, and (b) to expose their leaves to light. Climbing plants present four divi- sions, viz. : (i) Those which climb by the aid of rootlets, as the Ivy. (2) By the use of hooks, as the Bramble and the Yellow Bedstraw. (3) By twining stems, as the Convolvulus and the Hop. (4) By sensitive organs which come in contact with any structure and clasp it, as the Clematis and the Vine.
Rootlet-Climbers.- The Ivy climbs by means of adventitious roots which are produced from the stem. When these come in contact with a wall or the bark of a tree they give out a fluid, which by drying up causes the stem to adhere to the
support. The rootlets are produced on the shady side of the stem, and in older stems may not all be fixed to the support, but may be "dried up, forming shaggy beards (Fig. 22).
Hook-Climbers. — The Bramble is able to support itself by weaving its way through the trees which grow in its neighbour- hood. It is able to do this because it produces hooks, by the aid
FIG. 22. — Ivy climbing up a wall. R = Aerial roots.
26
BOTANY FOR BEGINNERS
CHAP.
of which it fixes itself to walls, trees and shrubs. Cleavers,
which is a struggling, rough and matted plant found in hedges,
is another good example of a plant which climbs by means of
hooks (Fig. 23). Stem -Climbers. — When the stem of the hop plant comes
out of the ground its first
two or three internodes grow
up erect. The young inter- nodes which are produced
from the top of the first- formed portion commence to
bend slowly and gracefully
to one side and travel
steadily round to every point
of the compass, describing
a complete circle in the
direction the minute hand
of a watch moves over its
face. Should the twining
stem of the Hop come in
contact with a support, the
part which it strikes is seized FlG- 23--The hooks of the Bramble.
by the hooks which are well
developed on the stem. The stem still grows at the apex and
goes on twining, thus climbing more and more about the
support. The Bindweed or Convolvulus also climbs by means
of twining stems, but these climb in the opposite direc- tion to the Hop, i.e., to- wards the left. The stems of the Hop and Honey- suckle turn round from the west through the south towards the east ; this is called twining to the right. The Scarlet Runner and
W
FIG. 24.— Diagram illustrating how plants twine. The left-hand figure shows how the Honeysuckle twines to the right ; the
ight-hand figure how the Convolvulus
wines to the left.
twines to the
the Bind-weed turn round
.from the west through the north towards the east ; this is termed twining to the left (Fig. 24). Plants which Climb with Sensitive Organs.— This
Ill
ANATOMY-STUDY OF THE SHOOT
27
division can be subdivided into two classes, w>., leaf-climbers and tendril-climbers.
A good example of a leaf climber is the familiar Clematis. The upper, younger internode of the Clematis goes wandering round and round in slow circles after the manner of the twining
FIG. 25. — Climbing stem of Honey- suckle. (One-fourth nat. size.)
FIG. 26. — Climbing stem of Con- volvulus. (One-fourth nat. size.)
plants. This brings the leaves in contact with the stems, twigs, or the trellis-work erected by the hand of man. Such objects as these are seized slowly but surely by the leaf-stalks of those leaves which come in contact with them. The leaf stalks are sensitive and turn round the object touched.
A tendril is another structure which is sensitive to touch and
28
BOTANY FOR BEGINNERS
CHAP.
Is used for climbing. These organs, with their ready response to any contact and their power of turning round and clinging to objects, are the most highly developed in the class of climbing plants. Tendrils are formed from various parts of plants ; thus, in the Passion flower it is a whole branch transformed ; the tendril of the Vine is a flower-stalk ; that of the Sweet Pea, the whole blade of a leaf ; that of the Cucumber and its allies arise
by the alteration of the leaf-like bodies found at the base of the leaf-stalk and known as stipules. The tendrils, like the twining stem, move round and round in search of a support.
Some tendrils, when their move- ments are arrested by a support, form adhesive masses at their free ends, as in the Virginian creeper, which is so often seen covering the sides of houses. Soon after the tendrils of the Virginian creeper have laid themselves down, as it were, upon a wall, their tips swell, become red and form little swollen cushions. On the parts in con- tact with the wall, small pro- jections are produced which in- sinuate themselves into every little crevice and seem to give out a cement which binds them to the support (Fig. 27).
R
FIG. 27. — Virginian Creeper. R, R, stem tendrils. (Three- fourths nat. size.)
EXPT. 1 8. — Obtain a piece of Ivy from an old wall ; examine it. Note the following points —
(i) That a portion of the wall has come away with the roots, (ii) That the roots grow on a portion of the stem which is turned away, from the light.
(iii) That the root dries up, and forms a beard on the stem.
EXPT. 19.— Examine branches of the Rose or Bramble. Notice— (i) The prickles ; pull one or two off and see how much of the branch comes away with them.
(ii) Prickles may be used for protection as well as for climbing.
Ill
ANATOMY— STUDY OF THE SHOOT
29
EXPT. 20. — Obtain a portion of the Hop-plant or Honeysuckle with its support. Note —
(i) How and in what direction the stem has moved. Compare with a piece of the Scarlet Runner and Bindweed.
(ii) Note the difference in the direction of twining.
EXPT. 21. — Obtain from a hedgerow or garden a piece of Clematis showing the sensitive leaf-stalks. Examine how the stalks clasp the support.
EXPT. 22. — Obtain a tendril-bearing plant, such as the Vine, Vetch, Sweet Pea, Cucumber, or Bryony. Examine to see what parts of the plant have been modified in the production of the tendril. Compare with a portion of the Virginian Creeper.
The Shape of the Stem. — Stems may be round or cylin- drical^ as in the Lily ; triangular, as in the flower stem of the Daffodil ; square, like the Deadnettle ; or ribbed, like the Wall- flower (Figs. 28 — 32).
FIG. 28. Round stem, with section.
FIG. 29. Square stem, with section.
FIG. 30.
Ribbed
stem, with
section.
FIG. 31. Triangular stem, with
section.
FIG. 32.
Coarsely- ribbed stem, with section.
Some stems are solid at the nodes, but hollow at the internodes, e.g.* FooFs-Parsley. Others are solid throughout as in the Wallflower.
Surface of the Stem.— Stems differ not only in their shapes but also as regards the nature of their surfaces. Many stems are completely covered with hairs, prickles, or thorns. If the surface is smooth, it is termed glabrous ; if hairs are present, hairy.
BOTANY FOR BEGINNERS
CHAP.
The Wallflower is covered with spindle-shaped hairs, and upon the Stock branched hairs are found.
In the Stinging Nettle large hairs for protection are found. When the tip of such a hair enters the finger it breaks off and a fluid is injected into the wound causing a well-known smarting sensation.
The surface of a stem may be covered with prickly structures, which may be produced by the modification of hairs, or other structures. The hooks on the stems of the Hop, Cleavers, arid
Borage are true hair-structures, be- cause they are de- veloped from the surface layer of the plant. The struc- tures found on the stem of the Sloe, and which are fo rm ed from branches which have undergone change so as to protect the plant from its enemies, are called thorns. The prickles of the Hawthorn are modified leaves ; they are, as a rule, termed spines. The prickles of the
Bramble and Rose are formed not only by the development of the surface covering of the plant, but also by a deeper layer which takes part in their formation. The name emergences may be given to them.
EXPT. 23. — Cut across the stems of the following so as to show their shape :— Wallflower (old stem), and flower stems of the Daffodil, Lily, Deadnettle, and Mignonette. Compare their shapes and notice if the stems are solid or hollow.
EXPT. 24.— Examine as many stems as possible to see if they are
FIG. 33. — Spines on the Hawthorn.
in ANATOMY— STUDY OF THE SHOOT 31
smooth or hairy. Similarly describe the surface of every stem met with. If this is done for a few weeks, the reader will have a very valuable series of notes.
EXPT. 25.— Collect a few branches of the following plants : Haw- thorn, Rose, Sloe, Bramble, Hop, Cleavers, Borage, and prickly Comfrey. Examine and make notes of the size of the prickles, thorns, spines, and emergences found on them. Sections should be made through the stem so as to show the connection of the covering with the underlying parts.
Leaves. — Leaves are developed as lateral outgrowths from the growing point of the stem. They are often said to be flattened out stems. They may be deciduous, that is, they may fall off from the stem each year ; or persistent, remaining on the tree for a number of years. The Oak produces the former kind of leaves and the Holly the latter.
Leaves are developed in regular order, the older ones being found on the base of the young twig and the younger ones near the apex. There are four kinds of leaves which grow on the stem. They are :—
Foliage-leaves, or the ordinary green leaves of the plant.
Scale-leaves, or those found covering the bud.
Bracteate-leaves are found close to the flower, which they as a general rule protect.
Floral-leaves ; some of these are coloured, and the flower is built up by them.
All these kinds of leaves are not found on every plant. Most plants possess foliage leaves, but the Dodder has only scale leaves. In the Lily of the Valley, the foliage leaves, bracts and floral leaves are all developed. In the Wallflower only the first and last are found.
EXPT. 26. — Collect branches of the Oak and Fir in winter. Notice that the twigs of the Oak are without leaves, but the Fir is well covered with them.
SUMMARY.
Shoot. — Built up of stem and leaf. The growing point is at the apex, and is surrounded by leaves.
A bud is an undeveloped shoot. There are three kinds of buds, viz. , stem-buds, leaf -buds, and flower-buds. The bud at the apex of a stem is called the terminal bud, and those behind lateral^ and if the latter
32 BOTANY FOR BEGINNERS CHAP.
are produced in the axils of the leaves they are axillary buds. An adventitious bud is one which is produced out of the regular order. A latent or dormant bud is one which remains undeveloped.
Tillering is a term which is used to describe what takes place when a plant produces a large number of branches from the base of the stem.
Plants can be divided into (i) A nnual plants ; these only live a single season. (2) Biennial plants ; these during their first year of growth produce foliage leaves and store up food, and during the second season produce flowers and seeds. They only live two years. (3) Perennial plants live three years or more.
The ascending axis produces leaves, and connects the leaves with the roots. The places on the stem from which leaves spring are termed nodes, and the space between two nodes is called an internode.
Stems. — There are three kinds of stems.
Herbaceous.
Soft and green, and die down each year.
Shrubby.
Hard and woody, not above twenty feet high.
Woody.
Woody.
These are hard and strong, and grow "Vvwo twenty feet high.
above
Aerial Stems grow above the ground. They can be divided into : The Runner, which creeps along the ground, like the Strawberry. The Offset creeps along the ground for a distance from the parent, then roots. The Stolon is a branch which takes root at its end. The Sticker is given off from an underground stem. The Erect Stem grows upright like the Oak.
Subterranean Stems grow beneath the ground and can be divided into : The Rhizome, which creeps along beneath the ground and pro- duces both roots and leaves. The Tuber is a swollen underground stem which grows from the end of a stolon. The Bulb is a fleshy under- ground bud, and is modified for the storing up of food for future use. The Corm is a solid, fleshy, underground stem.
Parasitic Stems are produced by parasites. A parasite is a plant which is too lazy to earn its own living, so lives on a host .plant. The Clover Dodder is a good example of such a plant.
Climbing Plants. — There are four classes of these plants. They are as follows : Rootlet Climbers, like the Ivy. Hook Climbers, like the Bramble. Stem Climbers, like the Hop and Convolvulus. Plants which climb with sensitive organs ; they can be divided into (a) leaf and (b] tendril climbers.
Stems. — They may be round, square, ribbed, and triangular. They may be smooth or hairy. The surface may be covered with spines or emergences.
Leaves are produced as outgrowths of the growing point of the stem. There are four kinds of leaves found growing on the stem : Folio ge Leaves are the ordinary green leaves of the plant. Scale Leaves are found on the roots and young buds. Bracteate Leaves are found at the base of the flowers. Floral Leaves are modified leaves which go to build up the flower.
in ANATOMY- STUDY OF THE SHOOT 33
QUESTIONS ON CHAPTER III.
1 i ) Of what use to the plant is the stem ? How can you distinguish a stem from a root ?
(2) What are the essential differences between a node and an internode ? Illustrate your answer by examples. (1884.)
(3) What is a rhizome, and how does it differ from a root? Explain the mode of annual growth in length of the rhizome of Solomon's Seal. (1885.)
(4) State what is meant by annual, biennial and perennial plants, giving examples. (1886.)
(5) What do you know about —
(a) The runner, (b) The rhizome,
(c\ The tuber, (d) The offset,
(e) The bulb, (/) The corm ?
(6) What kinds of stems are there ? Give examples.
(7) Where is the growing point of a shoot found, and how is it protected from injury ?
(8) If all the leaves on a Currant bush be plucked in spring, what will happen ?
(9) How are the knots found in thnber produced ?
(10) Define the term " tillering." When and how does tillering take place ?
( 1 1 ) What is a parasite ? Give an account of the mode of life of the Dodder.
(12) Give examples of plants which climb by means of tendrils, and explain how the tendrils act. (1887.)
(13) Give a classification of climbing plants. Why do plants climb ? How do they climb ?
(14) What is the structural difference between a prickle (as in the Rose) and a spine (as in the Blackthorn) ? (1881.)
CHAPTER IV
THE STUDY OF THE SHOOT (Continued)
Parts present in a Perfect Foliage Leaf.— In a perfect leaf the following parts are present.
The blade or the fully expanded portion of the leaf. I\\R petiole or the stalk of the leaf.
The Sheath which forms the base of the leaf. It is wider than the petiole, and may sheathe the stem.
In most cases the blade is present ; when other parts of the leaf are absent, the leaf is said to be sessile, as in the Wall- flower. If the sheath is not developed, but the blade and petiole are present, the leaf is called petiolate, as in the Cherry. If all the parts are present, as in the Pilewort and Arum, the leaf is perfect. Outgrowths may be produced from the base of the leaf, as in the Rose and the Pea ; these are termed Stipules. If stipules are present the leaf is said to be stipulate, and if they are absent exstipulate.
The Venation of Leaves.— The veins of a leaf form the framework by which the softer parts are supported ; they also bring the sap from the stem and distribute it to the cells of the leaf. Leaves may either be parallel or reticulate — veined. The former arrangement is found in monocotyledonous plants and the latter in dicotyledonous. In a parallel- veined leaf, the veins run parallel to one another from the base of the blade to
-B
FIG. 34.— Perfect leaf of Arum. B = blade ; P = peti- ole ; sh =sheath.
CH. IV
THE STUDY OF THE SHOOT
35
the apex, and they are connected by smaller cross veins, as in
the leaf of the Lily of the Valley. The reticulate-veined leaf
differs from the parallel-veined leaf
in possessing one or more midribs,
from which veins are produced
eventually uniting with one another
to give the leaf the appearance of
net-work. The Oak bears such a
reticulate-veined leaf (Fig. 36).
If the leaf only possesses one mid-rib, the leaf is said to be uni- costate. When the leaf is divided into a number of divisions, and each lobe possesses a mid-rib, it is said to be multicostate. The leaves of the Oak, Beech, Poppy, and Dan- delion, are unicostate, while the leaves of the Monkshood, Castor- oil plant, and Fig, are multicostate.
The veins of a leaf give it
strength ; it depends upon the mode of life of the plant what kind of leaves will be produced. Plants which grow in a very
FIG. 35. — Venation of a leaf.
FIG. 36.— Unicostate leaf of Oak.
FIG. 37. — Multicostate and palmate leaf of the Horse-Chestnut.
exposed position generally have narrower leaves than those which grow in sheltered places. Water plants with submerged
D 2
BOTANY FOR BEGINNERS
CHAP.
leaves have the veins finely divided so as to give mechanical support, as well as to expose as great a surface to the water as possible. In the case of marsh plants like the water Crowfoot, which has two kinds of leaves, it is only the submerged ones which are divided.
Ex FT. 27. — Collect a number of leaves and arrange them into —
(i) Two series according to their venation.
(ii) The two divisions, unicostate and multicostate.
Arrangement of Leaves on the Stem.— Leaves grow from the nodes of the stem, and the arrangement of these
FIG. 38. — Alternate leaves of Rhododendron.
FIG. 39. — Opposite leaves of Privet.
depends upon the length of the internodes and the size of the leaves. The leaves on a given plant are always inserted at points which bear a certain relation to one another, which may be expressed in a numerical manner. The arrangement of leaves on a stem is often spoken of as phyllotaxis. If one leaf only is produced at a given node, and from the node higher up the stem but on the opposite side another springs the phyllotaxis is said to be alternate, as in the Wallflower.
IV
THE STUDY OF THE SHOOT
37
When two leaves spring from the node and face each other, the arrangement is called opposite ; if the leaves higher up are placed at right angles to the first pair, the arrangement is called decussate — the Deadnettle is a good example of this. If more than two leaves are produced at a node, they are termed whorled leaves. The Bed-straw and Cleavers illustrate this arrange- ment.
The most common ar- rangements of leaves are the alternate, opposite, and whorled. The so- called alternate arrange-
Start of Spiral Twig ofOaJc .
FIG. 40. -Whorled leaves of Cleavers.
FIG. 41. — Diagram illustrating £ phyllo- taxis of Oak.
ment can be further investigated by drawing a spiral round the stem from one leaf until the leaf vertically above is reached. In the case of the Wallflower or Oak the spiral goes round the stem twice before the leaf vertically above is reached, and five leaves, not counting the leaf at which the spiral commenced, are touched by the -spiral. This is known as a £ arrangement. The same phyllotaxis is found in the Pear, Poplar, and Walnut. In the Plantainthe leaves form a $ phyllotaxis.
BOTANY FOR BEGINNERS
CHAP.
FIG. 42.— Diagram illustrating f phyllotaxis.
FIG. 43. — Diagram illustrating ^ phyllotaxis.
simple when the blade consists Elm, Holly, and Dead- nettle. The blade may be divided, but, unless it is cut down to the mid- rib, it is still a simple leaf. Compound leaves are cut into a number of distinct pieces, as in the Pea and the Ash. Each separate part of such a leaf is called a leaflet.
Simple Leaves. — Leaves vary much in shape or general outline. FIG.
EXPT. 28. — Collect and ex- amine branches of the Oak, Wallflower, Deadnettle, Bed- straw, and Elm. Determine their phyllotaxis, and mark on the stem the leaf-cycle or the cycle made in passing from one leaf to the leaf vertically above. This can be done with a piece of coloured chalk, and if the leaves are also numbered the arrangement will be seen at a glance.
Different Kinds of Foliage Leaves. — When the leaves spring from an underground stem, as in the Daisy and Dandelion, they are called radical leaves. If^ they grow on an aerial stem, as the leaves of the Oak and Wallflower, they are spoken of as cauline leaves.
Foliage leaves may be either simple or com- pound. Leaves are called of a single piece, as in the
44. — Radical leaves of the Primrose.
IV
THE STUDY OF THE SHOOT
39
Simple leaves receive the following names, according to the shape of the blade :—
Lanceolate ', when the leaf is from two to four times as long as it is broad and tapers at both ends, e.g., Wallflower (Fig. 45).
Ovate, when the broadest part is nearer the base than the apex, e.g. Guelder-Rose (Fig. 46).
Cordate, when the base is shaped like a heart, e.g. Lime (Fig. 47).
Sagittate, when the base possesses pointed ends extending like an arrow backwards, e.g. Convolvulus (Fig. 48).
Obovate, when the broadest end is nearer the apex than the base, e.g. as in some of the Rock- Roses, and leaflet of Wood-Sorrel (Fig. 49).
Fici. 45.— Lanceolate leaf of Wallflower.
Fig. 46.— Ovate leaf of Lilac. '
FIG. 47. — Cordate leaf of Deadnettle.
Oblanceolate, when the lanceolate leaf has a wider part which is nearer the apex than the base, e.g. Dog Violet and Spurge Laurel (Fig. 50).
Spatulate, when the leaf is like a spoon, with a rounded portion near the apex, e.g. Daisy.
Reniform, when the leaf is kidney-shaped, e.g. Ground Ivy (Fig. 52).
Linear, when the leaf is very long and narrow, e.g. most Grasses (Fig. 53).
Elliptical, when the leaf is oval, e.g Apple (Fig. 54).
Acicular, when shaped like a needle, e.g. Fir.
BOTANY FOR BEGINNERS
CHAP.
Many of the above terms are used to describe the shapes of the leaflets of compound leaves.
FIG. 48. — Sagittate FIG. 49. — Obovate FIG. 50. — Diagram FIG. 51. — Spatulate
leaf of Arum. leaflet of Wood- of Oblancaolate leaf of Daisy.
Sorrel. leaf.
Compound Leaves.— If the blade of the leaf is divided down to the mid-rib it is said to be compound. The separate parts of the blades are called leaflets ; these are given off from
FIG. 52 — Reniform leaf of Ground Ivy.
FIG. 53. — Diagram of linear leaf.
FIG. 54.— Elliptical leaf of Apple.
the mid-rib. The leaflets separate from the mid-rib or petiole in the same way that the entire leaf separates from the stem, /.<?., without tearing. They may be pinnately or palmately divided. The following are examples of the latter kind.
IV
THE STUDY OF THE SHOOT
Ternate or trifoliate, the leaf is built up of three leaflets, as in the Clover and Wood-Sorrel (Fig. 55).
Bitemate, when the leaf is ternate, but each division is divided again ; in fact, three leaflets divided into three leaflets, as in the Baneberryor Herb Christopher. Palmate, when the leaflets radiate from the leaf-stalk like fingers from the palm of the hand, e.g., Horse- Chestnut (Fig. 37),
When the leaflets are arranged along each side of the midrib, they are said to be like a feather or pinnate.
FIG. 55.— Ternate leaf of Wood-Sorrel.
FIG. 56. — Ternate leaf of Strawberry.
FIG. 57.— Biternate leaf of Baneberry.
There are two kinds of pinnately divided leaves — those with an equal number of leaflets along each side of the mid-rib, and those with an odd leaflet. The former are called paripinnate, and the latter iinparipinnate.
Paripinnate, when there are an equal number of leaflets on each side of the mid-rib, as in the Bitter Vetch.
42
BOTANY FOR BEGINNERS
CHAP.
Imparipinnate, when there is an odd leaflet, as in the Rose and Robinia (Fig. 58).
Bipinnate, when the leaflet is again divided, as in the common Meadow Rue and Acacia (Fig. 59).
Tripinnate, when the division is carried a little farther and each part is in three, as in the Lesser Meadow Rue.
The Margin of Leaves.— The margin of leaves vary in different plants. The following terms are used to describe them : —
Entire, if the margin is undivided, as in the Wallflower (Fig. 60).
FIG. 58. — Imparipinnate leaf of Robinia.
FIG. 59.— Bipinnate leaf of Acacia.
Serrate, if the margin is divided up into teeth-like divisions, like a saw, and they point towards the apex, the above term is used, ^>.,Deadnettle.
Biserrate, if the teeth are again divided, as in the Elm.
Crenate, if the teeth are rounded, as in the Ground Ivy.
Dentate, if the teeth point outwards, as in the Guelder Rose.
IV
THE STUDY OF THE SHOOT
43
Ciliated, if the margin is fringed with fine hairs like the Beech.
Spiny , if the teeth are long and very sharp, as in the Holly.
Apex of the Leaf— The apex of the leaf may be sharply pointed, when it is called acute ; if blunt, Obtuse ; and if the end is long and pointed, acuminate (Fig. 61).
Further Kinds of Simple Leaves.— When the leaf is
\
FIG. 60. — Diagram of margin of leaves, i, biserrate ; 2, serrate ; 3, crenate 4, spiny ; 5, entire ; 6, dentate ; 7, sinuate.
split up into a number of divisions, and these do not cut down to the mid-rib, the following terms are used : —
Palmatisect, if the ends extend nearly to the base, e.g., Monkshood.
Palmatifid, if the cuts extend about halfway from the margin to the base of the leaf, as in the Castor Oil plant.
Palmate, if in the palmatifid leaf the number of divisions is five, as in the Maple.
44
BOTANY FOR BEGINNERS
CHAP.
Pinnatisect, if the divisions extend nearly to the mid-rib, as in the Poppy.
Pinnatifid, if the cuts extend about half way from the margin
B
FIG. 61. — Diagram of apex of leaves. A, acuminate ; B, obtuse ; C, acute ; D, mucronate ; E, retuse ; F, emarginate.
to the midrib, as in the Welsh Poppy, and in some of the leaves of the Mignonette.
Lobed Leaves. These, according to the number of lobes, may be trifid) trilobed, five-lobed, &c.
EXPT. 29. — Make a collection of leaves. Note and compare their shapes with the figures in the book.
The leaves can be dried by pressing them widi heavy weights between the leaves of a blotting book or even between sheets of note paper. If the sheets of paper be changed every day until the leaves are perfectly
THE STUDY OF THE SHOOT 45
dry, the leaves can be mounted on sheets of card board, or on special papers such as the following : —
.6 in
4 in
Shape. Margin. Apex. Venation. Name of plant.
EXPT. 30. — Try and cut out in paper the different forms of any leaves which may be obtained. This can be done by laying the leaf on a sheet of white paper and tracing on the paper with a fine pointed pencil the outline of the leaf. Cut along the lines so made with a sharp pair of scissors. The name of the leaf and its shape can be marked on the model. The pupil will soon discover how difficult it is to describe the leaf with accuracy, and will also apprehend the greater truth that there are probably not two leaves alike.
EXPT. 31. — Examine every leaf, spine, and tendril you can obtain.
Stipules. — These, as we have already seen, are outgrowths at the base of the leaf. The texture and colour of stipules vary ; thus, if their function is to protect the young leaves in the bud, they may be brown or yellow in colour ; if they are used for assimilation, that is, to provide nourishment for the plant, they are green in colour, and large and leaf-like in form.
There may be two stipules, one on each side of the leaf, as in the Pea and Pansy. In some of the Bed-straws the stipules are large and are often mistaken for leaves ; in fact, they appear to form whorls with the leaves. The stipules are membranous in the Rose leaf, where they are represented by a series of teeth along each side of the base, and are called adnate stipules. Where
46
BOTANY FOR BEGINNERS
CHAP.
the stipules unite in the leaf-axil they are called axillary^ as in the Pea (Fig. 62).
Scale Leaves. — Scale leaves possess a far simpler structure than foliage leaves. They have no leaf-stalk, and are directly attached to the stem. Their principal function is to protect the young buds, and they are the only leaves found on under- ground stems. A few parasitic plants, such as the Broom Rape
FIG. 62.— Leaf of Pea. Fi, flower- stalk ; SP, stipules ; T, tendrils.
FIG. 63.— Leaf of Rose. L, leaflets ; P, petiole ; sf, stipules.
which grows on the roots of plants, do not possess any other kinds of leaves.
Bracteate Leaves. — Bracteate leaves resemble scale leaves both in structure and function. They grow at the base of the stem upon which the flowers are produced. When present the plant is said to be bracteate, if they are absent, ebracteate. Bracts may be scaly, leafy, membranous, woody, or coloured. When the bracts are arranged in a circle, as in the Dandelion, they form an involucre. If the bracts form a solid cup, as in the
IV
THE STUDY OF THE SHOOT
47
acorn, they form a cupule. When a single bract is large and protects a series of flowers it is called a Spathe, e.g., the Arum.
EXPT. 32. — Examine the leaf of a Pea and find the stipules. Note — The stipules are large and leaf-like. Observe how the end of the mid- rib of the compound leaf is converted into a tendril. Compare with the stipules of a Rose leaf.
EXPT. 33. — Note the size, shape, and characters of as many scale leaves as possible during spring, when the buds are opening.
FIG. 64. — Transverse section of leaf-bud of Water Lily, (x 6.)
Fig. 65.— Bracteate leaf of Narcissus. B, bract.
FIG. 66. — Transverse section through leaf-bud of Lilac. (X 5.)
Floral Leaves. — Floral leaves are modified leaves which go to build up the flowers of a flowering plant.
Vernation. — The way in which the young leaves are folded in the bud is called vernation or prcefoliation. This differs in different plants, and will be considered under two heads, viz., (a] the folding of the individual leaf in the bud ; and (V) the folding of the several leaves in the bud.
48
BOTANY FOR BEGINNERS
CHAP.
The arrangement of the individual leaf in the bud is shown below in a tabular form : —
i. — If the leaf is not folded at all, the vernation \^ plane.
2. — If the leaf is folded along the mid-rib, it is conduplicate, e.g.) Bean.
3. — If the leaf is folded into a number of longitudinal or oblique pleats, it is plicate, e.g., Beech.
4. — If the leaf is folded in all directions, it is crumpled, e.g., Poppy.
5. — If the leaf is folded inwards towards the mid-rib, it is involute, e.g., Violet.
FIG. 67.— Transverse sec- tion of leaf-bud of Ash. (X7-)
FIG. 68.— Transverse section through leaf- bud of Beech. (X6.)
6. — If the leaf is folded backwards towards the mid-rib, it is revolute, e.g.", Dock.
7. — If the leaf is folded up from one side to the other, it is convolute, e.g., Banana.
The arrangement of the several leaves in the bud is shown below : —
i. — If the leaves in a bud just touch by their margins, the vernation is valvate.
2. — If the leaves in a bud overlap each other, it is imbricated.
3. — If the leaves in a bud overlap each other in regular order, it is twisted or contorted.
4. — If the outer conduplicated leaves in a bud enclose those within in regular order, it is equitant.
IV
THE STUDY OF THE SHOOT
49
5. — If half of one conduplicated leaf enfolds another, it is seini-equitant.
6. — If one convolute leaf is rolled around another, it is supervolute.
EXPT. 34. — Cut a transverse section of any leaf- buds met with. Note—
(i) The arrangement of the individual leaves in the bud.
(ii) The arrangement of the several leaves in the bud.
(iii) The arrangement of the parts in the buds. Show it by sketches.
SUMMARY
A Perfect leaf consists of a sheath, petiole, and blade. If the blade is the only part present, the leaf is said to be sessile, and petiolate when the blade and petiole are developed.
Stipules are outgrowths at . the base of the leaf. Leaves can be exstipulate or stipulate.
Venation of leaves — two kinds — parallel and reticulate.
Phyllotaxis is the arrangement of leaves on a stem. The common arrangements are alternate, opposite, and whorled.
Foliage Leaves may be simple or compound. In the former the blade is not divided down to the mid-rib, but in the latter kind the blade is cut up in separate or distinct parts.
FIG. 69. — Transverse section of leaf-bud of Sycamore. (X4.)
Simple leaves may be Lanceolate. Oblanceolate. Ovate. Cordate. Sagittate. Spatulate.
Obovate. Reniform. Linear. Elliptical. Acicular.
Compound leaves may be Ternate. Paripinnate.
Biternate. Irnparipinnate. Palmate. Bipinnate.
Tripinnate.
The Margin of Leaves may be— (i) Entire, (2) Serrate, (3) Biserrate, (4) Crenate, (5) Dentate, (6) Ciliated, (7) Spiny.
The Apex may be— (i) Acute, (2) Obtuse, (3) Acuminate.
The Margin may be divided as— (i) Palmatisect, (2) Pinnatifid, (3) Pinnatisect, (4) Palmatifid, (5) Palmate, (6) Lobed.
Stipules may be leaf-like, or membranous.
Scale Leaves.— These are found to be modified leaves ; they protect the buds from injury.
Bracteate Leaves. —These are found at the base of the flowers, and may form an involucre, cupule, or spathe.
50 BOTANY FOR BEGINNERS CH. iv
Floral Leaves. — From these various parts of the flowers are formed. They can be divided into four kinds. Vernation or Praefoliation is the folding of the leaves in the bud.
QUESTIONS ON CHAPTER IV.
(1) What is a leaf? Excluding the leaves forming the flower, we have three kinds occupying different positions on the stem in the higher plants. Briefly describe these.
(2) (a) What parts are present in a perfect foliage leaf? (b] What kinds of venation are found in leaves ? »
(3) Give instances of leaves which are only imperfectly developed. What useful purposes may they serve in such cases? (1882.)
(4) What is the general plan of arrangement of leaves on a stem ? Why is it the most advantageous to the plant ? (1881.)
(5) Give a botanical description of the part, in each of the following plants, which is commonly used as food : the potato, the onion, the turnip, and the carrot. (1887.)
(6) Describe, with examples, the principal forms of compound leaves. What is the difference between a simple and a compound leaf? (1890.)
(7) Explain, with examples, the following terms : — Bract, stipule, pinna, petiole, peduncle. (1896.)
. (8) What are stipules ? Describe the stipules of the Rose and the Sweet Pea.
(9) How do the leaves of the Oak differ from the leaves of the Clover ?
(10) Describe the general structure of the leaf-bud, explaining the meaning of the term " vernation." What is the usual position in which buds are developed on the stem? (1891.)
CHAPTER V
ANATOMY— STUDY OF ROOTS
Descending axis.— The descending axis, or root, is the part of the plant which grows downwards, fixes it into the soil, and takes from the ground water in which minerals are dissolved. The root can be distinguished from the stem in the following way : —
ROOT.
1. The root produces neither leaves nor buds.
2. The root as a rule grows downwards.
3. The growing point of a root is protected by a sheath which is called the Boot cap.
4. The root produces small hairs, which absorb from the soil the water and minerals required by the plant for its growth.
5. Roots grow away from the light.
EXPT. 35. — Dig up a Deadnettle and examine it.
(i) The roots bear neither leaves nor buds.
(ii) The stem produces both.
(iii) The hairs on the stem, which are close set and are used to protect the plants from cold currents of air and from insect pests.
(iv) The very minute and soft hairs on the roots. These can be best seen if the root be held up between the eye and the light and looked at through a hand-lens.
£ 2
STEM.
1. The stem produces both leaves and buds.
2. The stem as a rule grows upwards.
3. The growing point of the stem is protected by scale leaves.
4. The stem produces hairs ; but these are as a rule used for protection, and not for obtain- ing food.
5. Stems grow towards the light.
Note—
BOTANY FOR BEGINNERS
CHAP.
EXPT. 36. — Take a few Beans and soak them in water for twenty- four hours. With a sharp knife cut longitudinal slices from the radicle and place them on a glass slip, such as is used for microscope work. Hold the glass slip between the eye and a strong light and place the hand-lens up to the eye. Move the sections first towards the lens and then away from it, until they appear clear. Near the apex of the radicle a dark inner portion and an outer lighter part can be made out. The dark portion is the growing point, and the lighter part the root-cap.
The Primary Roots.— The root pro- duced by the elongation of the radicle is termed a primary root. When the primary root persists and continues to grow it is called a tap-root. The Oak, Bean, and Wallflower produce tap roots. Branches are produced from the primary root in regu- lar order, the oldest being found towards its base, i.e., near the apex or growing point.
The Secondary Roots.— The lateral branches of the primary root are termed secondary roots. They differ from the branches of the stem in not being produced in the axil of leaves, nor from buds ; but they are formed in regular order. Each plant produces a definite number of rows of rootlets, which are arranged longitudinally, the roots in each row being accurately one above the other. The secondary roots grow horizontally or somewhat obliquely, not straight down like primary roots, and in this way the roots between them parcel out the soil. In the Wallflower there are four rows of roots, which strike out north, south, east and west, and it is clear that between them there is always unoccupied ground. This unoccupied ground is worked by roots produced from secondary roots and known as tertiary. They have no definite direction of growth, but spread outwards, upwards, and in all directions, thus reaching every part of the vacant soil.
EXPT. 37. — Obtain a Wallflower plant with perfect roots. Wash the roots in water so as to remove the soil. Examine the roots and observe — (i) The primary root.
(ii) The secondary roots forming four rows, (iii) The tertiary roots growing from the secondary roots.
FIG. 70.— A Mustard seedling, showing root - hairs and cotyledons.
ANATOMY— STUDY OF ROOTS
53
EXPT. 38. — Compare the roots of the Deadnettle, or any other plant which can be obtained, with the Wallflower, and note the number of rows of secondary roots.
Adventitious Boots. — The roots which are produced without any definite order from stems, leaves and roots are termed adventitious. In most monocotyledonous plants the primary root is either very short or ceases to grow soon after it leaves the seed. Its place is taken by an immense number of adventitious roots which spring from the stem. When gardeners place cuttings in the soil, they are said to " strike " when they
FIG. 71. — The fibrous roots of a Grass.
FIG. 72. — Branches of a Gooseberry bush producing adventitious roots.
take root. This is brought about by adventitious roots being produced from the nodes of the stem which is pushed into the soil.
Clinging Roots. — When adventitious roots are used for climbing as in the Ivy, they are called climbing or clinging roots. Roots of this kind are very highly developed in many tropical plants like the Orchids.
54 BOTANY FOR BEGINNERS CHAP.
Such roots simply cling to the bark of trees, they take nothing from the plant on which it grows. Some water plants produce a large number of roots which float in the water and help to support or moor the plant. The Duckweed, which grows in many of our ponds, is a good example.
EXPT. 39. — Dig up a Grass plant from a field, and examine the roots. Note—
(i) The tap-root is either absent or very short.
(ii) A large number of roots, which seem to come from either the top of the root or from the stem, and grow without any regular order, can easily be made out. They are called adventitious roots. They are also fibrous roots.
Aerial Roots. — Adventitious roots which hang down in the air are called aerial roots. Epiphytes are plants which possess such aerial roots. The aerial roots of some plants can obtain water from the atmosphere and dissolve any mineral matter which may be blown against them. Many Tree Ferns, Aroids, and Orchids are epiphytes. The Vine may, in some cases, produce aerial roots which hang from the stem in rich profusion and most likely help to obtain water for the plant. Some aerial roots are green, and perform the same work as leaves. They may reach the ground and take root as in the Banyan tree. The Ivy clings to the bark of trees and to old walls by means of aerial roots which are produced from the shady side of the stem.
Water Roots. — The roots of plants which float or grow in water are known as water roots. They may be developed either from stems with floating foliage leaves, or from stems with sub- merged leaves. Floating roots never penetrate even the mud at the bottom of a pond : but the roots of marsh plants go right down into the mud. The ordinary roots of Willows, Alders, and Elms, growing along the sides of streams, often grow from the bank into the water in which they float. Water roots do not produce root hairs.
EXPT. 40. — Obtain a Hyacinth bulb, and place it in a vase of water. Make up the loss of water which will take place by a solution1 con- taining—
Potassium nitrate . I gram. Calcium phosphate \ gram. Sodium chloride . . \ ,, Water . . . .1 litre Calcium sulphate . . | ,, Iron chloride . . a few drops Magnesium sulphate. \ ,,
1 Any chemist will make up this solution.
ANATOMY— STUDY OF ROOTS 55
Such a solution contains everything necessary for the growth of a plant. Note how the bulb produces water roots, which obtain from the solution the substances required by the plant for its growth. Observe the growth of leaves and flowers. This experiment shows that roots, which under natural conditions live in soil, can change their mode of life and become water roots.
EXPT. 41. — Cut a slip from any plant, (the garden Geranium will do), so as to leave at least three nodes with leaves and one without. Place the slip in a bottle with some of the solution used in the last experiment.
Observe that roots develop in the water from the nodes. Keep the bottle warm ; it will soon be filled .with roots. These roots are adventitious and aquatic.
Parasitic Roots.— The roots of those plants which pene- trate a host plant, and extract nourishment from it, are called parasitic. The Mistletoe, which grows on Apple, Fir, and
FIG. 73. — St, stem of Apple. S, shoot of Mistletoe ; R, roots of Mistletoe. (One-twelfth nat. size.)
Poplar trees is a parasite. Mistletoe is very plentiful in our homes about Christmas time, and most persons know its berries. Thrushes feed on these berries, and the seeds enclosed in the fruit are protected from the digestive juices by a hard covering. They consequently pass out of the digestive tube without undergoing any change ; the droppings of the Thrush are
BOTANY FOR BEGINNERS
CHAP.
generally voided from the upper branches of trees and carry the seeds with them. The droppings and the seeds which are enclosed in them cling to the branches. The seeds germinate and the radicle which is produced is pressed closed to the bark and cemented there (Fig. 73).
The Eye-bright, so common in fields, produces suckers on its root which attach themselves to the roots of grasses and extract nourishment from them. The Yellow-rattle, Lousewort, COW-
FIG. 74. — Conical root of Carrot.
FIG. 75. — Napiform root of Turnip.
wheat, Toothwort, and Broom-Rape, are all parasites growing on the roots of plants.
EXPT. 42. — Pull up a few plants of Eye-bright and examine their roots. Find the suckers, which appear as little white knobs on the roots ; they are always found on the secondary roots.
Modified Boots. — Roots may be modified for the storing up of reserve materials, often becoming large and fleshy, as in the
ANATOMY— STUDY OF ROOTS
57
case of the Turnip. Roots of this description belong to biennial plants. The principal shapes of modified roots are as follows : —
i. — Conical^ when broad near the stem and tapering towards the tip, as in the Carrot (Fig. 74).
2. — Napiform, when shaped like a Turnip. The Swede usually has, at the crown of the root, a neck from which the leaves spring. This is absent in the Turnip (Fig. 75).
3. — Fusiform, when the root tapers both near the stem and towards the apex, e.g., Radish (Fig. 76).
FIG. 76. — Fusiform root of Radish.
FIG. 77.— Nodular or tubercular root of Pilewort.
4. — Tubercular, when the rootlets are swollen and round, as in the Pilewort (Fig. 77).
EXPT. 43.— Obtain the roots of the Turnip, Carrot, and Radish. Make sketches illustrating their shape, and mark on them the reduction in size which you make. This can be done by measuring the size of the root, and then the drawing . If these be compared, the reduction can be found. The pupil should do this in all sketches made.
EXPT. 44. — Dig up, either in March or April, the roots of the Pile-
58 BOTANY FOR BEGINNERS CHAP.
wort. This plant can be distinguished from the common Buttercup, because —
(i) Its leaves are cordate and perfect ; in the Buttercup the leaves are very much divided, and the segments are lobed.
(ii) The petals vary in number from eight to ten ; in the Buttercup there are only five. Examine the roots and note the swollen fibres ; these are used for storing up reserve materials. These are tubercular roots.
Uses of Boots. — Roots perform various functions which can be arranged in a tabular form.
1. Roots fix the plant in the soil. The roots can anchor a tree like the Oak so that the strongest wind cannot blow it over. In many cases the roots of grass-like plants are used by engineers, to bind together the soil along an embankment, and so keep it from falling, as on the West Coast of Lancashire and in North Italy.
2. Roots obtain nourishment from the soil. The roots parcel out the soil so that nutritive materials can be extracted from every part by the root-hairs. All the water given out by the leaves of a plant is obtained by the root-hairs from the soil. The roots make good the loss of water which takes place through the leaves.
3. Roots may be used as a store-house for material to enable the plant to produce flowers and seeds during the next season. In this case the roots are swollen and large.
4. Roots may be used for climbing, floating, or to enter a host plant. The shape, size, and method of growth of roots will depend upon their function.
EXPT. 45. — Obtain any plant growing in a plant pot. Cover over the soil, either with card-board or tin-foil, to prevent evaporation from the pot. Place the plant beneath a glass globe, and expose to light in a window sill. Note that the inside of the glass is soon covered with moisture. This is given out by the leaves, and the loss can only be made good by the water taken in by the roots.
Movements of Roots.— The younger portions of the roots are all in a constant state of motion. When the radicle leaves the seed it commences to move, and so long as life lasts the tip of the root will go on moving round and round in search of certain substances or conditions. The force exerted by a young radicle when growing is very great ; in twenty-four hours it causes a downward pressure equal to lifting a weight of a
v ANATOMY— STUDY OF ROOTS 59
quarter of a pound. Roots not only move in the direction of least resistance, but also towards damp and away from dry soil.
The use of these movements to the plant cannot be over- estimated. If the root made its way through the soil in a perfectly straight line, not half the favourable spots for food would be touched ; the spiral or circular movements of the root ensure its contact with the best sources of food in the soil. The tip of the root is also very tender and liable to be injured, and the movement from side to side enables it to find the path along which there is least danger to the growing point.
EXPT. 46. — Take a few Beans or Peas and germinate them on damp sawdust. When the radicle appears through the micropyle, turn the seeds over so that the radicle points upwards. Under another radicle place a piece of glass. Notice how the radicles act.
EXPT. 47. — Using the Beans or Peas germinated above,
(i) Cut off the root-tip of a radicle, so as to separate it just above the growing point.
(ii) Place a piece of post card on one side of the tip of a radicle, and on the other side a piece of tissue paper. This can be done by using a solution of shellac.
(iii) Cut slices from a few radicles, so as to remove a longitudinal layer from one side. Great care must be taken not to fix the card too far away from the tip or the radicle will turn towards the card, not away from it. Make notes of the results.
EXPT. 48. — Replace one of the sides of a box with a piece of glass. Fill up the box with alternating layers of sand, sawdust, clay, and peat. Sow mustard seeds or the seeds of any quick growing plants. Cover up the front of the box with a piece of cardboard. Keep the box warm and damp. When the seed leaves are well up in the air, place the box on a window sill. Remove the cardboard from day to day, to see how the roots are placed against the glass.
EXPT. 49. — Take the bottom out of a box, and nail on in place of the bottom a piece of wire netting with holes of about a quarter of an inch in diameter. Fill the box up with soil, placing the largest particles at the bottom. Grow plants as in Expt. 48. Hang the box up in a window and keep the soil moist. Note —
(i) The roots will pass out through the wire netting.
(ii) Many, if not all, will bend up and pass again into the box. This shows that the radicle or roots like darkness better than light. In fact, nearly all roots grow away from the light.
SUMMARY.
Roots can be divided into —
Primary roots. — A primary root is produced when the radicle goes on growing. Thus, all primary roots are produced by the elongation of
60 BOTANY FOR BEGINNERS CHAP, v
radicles. Those roots which are formed from the primary roots are called secondary roots. When roots grow out of the secondary roots they are known as tertiary roots.
Other kinds of Roots. — Adventitious roots are produced from stems, leaves, and roots without any regular order. Clinging roots are adven- titious roots used to fix a plant to a support. Aerial roots hang down in the air and take water from it, or enable a plant to climb. Water roots are produced by water-plants, and do not produce root-hairs. Parasitic roots penetrate into a host-plant and extract nourishment from it. Modified roots have undergone a change, so as to serve as a store- house of reserve material.
Shapes of Roots. — May be conical, napiform, fusiform, tubercular, fibrous.
Uses of Roots. — (a] They anchor the plant to the soil, (b) They obtain nourishment from the soil, (c) Food may be stored up in them. (d) They may be used for climbing, &c.
Movements of Roots. — Roots are always moving from place to place, so as to find food and the line of least resistance.
QUESTIONS ON CHAPTER V.
(1) Describe and explain, with reference to examples, the peculiarities of the roots of biennial plants. (1890. )
(2) What is a growing point? How does the growing point of a root differ from that of the stem ? ( 1 889. )
(3) Briefly describe, giving examples, the principal kinds of roots ; and explain what are the functions which the various kinds of roots are specially adapted to perform.
(4) How do roots parcel out the soil ? Give examples.
(5) Give sketches showing (a) conical, (b} napiform, (c) fusiform roots.
(6) What is an adventitious root ? Mention plants which produce such roots, and give an account of their function.
(7) What is a parasite ? How do the seeds of the Mistletoe find their way to the host plant ? How does the seed act when it germinates ?
(8) What is a root parasite ? Give examples.
(9) Of what use is a root ? In what circumstances may a plant exist without one ?
(10) Explain why the root of a turnip first grows faster than the stem, and then stops while the stem grows.
(n) Give an account of experiments which you have performed to show how roots move.
(12) In preparing sketches you have to show the scale. What is meant by the scale, and how can it be determined ?
CHAPTER VI
SECTION?, HOW TO PREPARE AND EXAMINE THEM
Sections. — To fully investigate the internal structure of a plant or its members, it is necessary to cut sections of the plant in various directions. A piece cut out of a stem is called a section. If the stem is cut across at right angles to its long axis it is called a trans- verse section. When the stem is cut along its long axis, the section made is termed longitudinal. There are two kinds of longitudinal sections, radial and tan- gential. A radial longitudinal section is one which passes through the organic centre of the stem. A tangential section can be made lengthways through the stem, but does not pass through the cen- tre. This is illustrated by Figs. 78, 79, 80 and 8 1. When a piece is cut out of a stem in the plane A, Fig. 78, the section is transverse. Such a section is shown in Fig. 79. If the cut is made through B, Fig. 78, it passes through the organic
centre, and is a radial longitudinal section, as shown in Fig. 80. The tangential section can be made through the plane C, Fig. 78. This is shown in Fig. 81.
To make good sections either a very sharp knife or a razor will be necessary. The shape of the blade will depend upon the size of the proposed section ; if the area of the section is small, a hollow-ground razor or knife will give the best results, but for
FIG. 78. — Diagram illus- trating how to cut sec- tions. A cut along the line A gives a transverse section : along plane B, a radial section : and along C, a tangential section.
62
BOTANY FOR BEGINNERS
CHAP.
large flat sections a cutting instrument with a flat side must be used. The section when made may be so thin that light can
FIG. 75. — A transverse section, cut through A, Fig. 78.
FIG. 80. — A radial sec- tion, cut through B, Fig. 78.
FIG.
nge
section, cut through C, Fig. 78.
pass through it, when it is said to be transparent. If the section is thick and no light can pass through it, it is called opaque.
EXPT. 50. — Take a long kidney potato and cut sections from it; they can be made in three directions, as fol- lows—
(i) At right angles to its long axis ; this will be a transverse section.
(ii) Parallel to its long axis, and passing through the centre ; this will be a radial longitudinal section.
(iii) Parallel to its long axis, but not passing through the centre ; this will be a tangential section.
Mounting Specimens. — After the sections have been cut they must be mounted on ordinary microscopic slips. These are pieces of glass three inches long by one wide. All fresh specimens can be mounted in water for examination by the microscope, but for examination by a hand lens the dry . object can often be used. Great care
FIG. 82.— Transverse section J
through a square stem. must be taken to have both the micro- scopic slip, and objects used in pre- paring the specimens, perfectly clean, for the slightest amount of dirt will spoil the section. In mounting the object in fluid only a small drop of it should be used, just sufficient
HOW TO PREPARE AND EXAMINE SECTIONS 63
to cover the object. For examination under the microscope, the section must be covered with a cover-glass ; these can be obtained of different sizes, the one in general use being ^ of an inch in diameter.
If the plant from which the sections have to be prepared has been kept in spirits, they must be mounted either in alcohol or glycerine. The section must never be allowed to dry ; if it does, air fills up the cells, and the air bubbles, as they are called, make the specimen appear very dark.
(1) Do not begin to cut sections until you are quite certain what kind you require. If the sections are to be viewed by the compound microscope, keep the razor or knife wet by dipping it before each cut into a glass of water for fresh specimens, and in spirits for materials which have been preserved in alcohol.
(2) Keep the microscope perfectly clean, and be careful that no mounting fluid finds its way on to the stage, lens, or any parts of the instrument.
(3) In mounting the specimen, only just sufficient of the mounting medium must be used to cover the object. When the cover-glass is put on, it must on no account be allowed to drop ; one edge must first touch the mounting fluid and be slowly lowered into position, so as to spread out the medium and drive out the air. This can be done by using a needle or pin to support the cover-glass, and with the thumb and finger of the left hand guide it into position as the needle or pin is slowly withdrawn.
(4) Always keep the section wet so as to avoid air-bubbles. If air- bubbles are found in a specimen, they may be removed by gently warming the slide by placing it over ajar containing hot -water.
(5) If the specimen is intended for future use be careful to label it, and write on this label the name of plant, portion of plant, direction of section, mounting fluid, and date.
EXPT. 51. — Take a glass slip, and with a dipping rod place a single drop of water in the centre. Now place a cover-glass over the drop of water. This can be done by using a needle or pin to support the cover- glass, and with the thumb and finger of the left hand guide the cover- glass into position, at the same time slowly withdrawing the needle or pin. After a few attempts the pupil will be able to spread out the drop so as to fill the entire space beneath the cover-glass.
The Structure and use of a Hand-Lens.— A lens is a transparent substance, usually formed of glass, and is shaped so as to change the direction of the rays of light which pass through it. A lens appears to magnify or diminish the size of objects seen through it. A hand-lens is a piece of glass, suitably mounted, which possesses the property of magnifying objects.
64
BOTANY FOR BEGINNERS
CHAP,
One of the best and cheapest for botanical work is shown in Fig. 83. It is called a triplet, because there are three lenses mounted so that each one can be used by itself, or in combina- tion with the others. To use such a lens to view a transparent object it is necessary to place the lens close to the eye and to move the specimen about until it appears bright and clear. The object is said to be in focus when it is best seen. If the specimen to be examined is opaque, the best way to observe it is to move both the lens and object until a good view is obtained. Transparent objects can be seen best with all the three lenses as
Fig. 83. — Diagram illus- trating hand - lens, i = low power. 2 = medium power. 3 = high power.
FIG. 84.
Diagram
showing position of lens when the highest
power is used.
Diagram show- ing position of
lens when
medium power
is used.
FIG. 86.— Diagram illus trating how to focus a hand-lens. A, the dis- tance of the object from the lens when in focus with the low power ; B, with me- dium ; and C, with high power.
shown in Fig. 84, but if the objects are opaque, with either lenses i or 2, or i and 2 combined, as in Fig. 85. In Fig. 86, the edges of the lenses are shown, and A, B, and C, indicates the relative distances at which a specimen may be viewed by i, i and 2 and i, 2, 3, respectively.
EXPT. 52. — Place a little cotton wool between two microscope slips, and with the hand-lens find out the position in which it has to be held so as to focus it with (i) the lower power, (ii) the medium power, (iii) the highest power.
vi HOW TO PREPARE AND EXAMINE SECTIONS 65
Cells. — If a thin transverse section of the stem of the sun- flower be made, and examined with a hand-lens, a number of openings will be seen ; these represent the elementary parts of the plant, and are called cells. The portion of the cell which surrounds the soft material is called the cell- wall, and in our section is the most prominent part of the cell. The soft material receives the name of protoplasm, and is the most important part of the cell. All plants are built up of cells, and these are arranged to form definite structures, which receive the name of tissues.
EXPT. 53. — Obtain a ripe Tomato and mount a small portion of the inner pulp without water, and examine with a lens. Note — the cells are very large and oval, the cell-walls are very thin, and a thin protoplasmic lining can be seen.
EXPT. 54. — Sow some seeds of the Sunflower in soil, and when the stem is about six inches in length, cut transverse sections of it. These should be placed in a watch-glass with a fifty % solution of alcohol to clear them. Mount the thinnest section in glycerine and examine with a lens. The cells are large and filled with protoplasm, and are arranged in definite groups,
EXPT. 55. — From a small Beetroot cut a thin transverse section, mount on a glass slip and examine with a hand-lens. Notice the cells are filled with coloured cell-sap. Place the section in alcohol for a few minutes and examine again ; the coloured cell-sap will have oozed out. This is due to the spirits having killed the protoplasm.
EXPT. 56. — Cut a thin section from a Potato, mount and hold it on the blade of the knife so that a portion is exposed to the light ; examine with a hand- lens. Note the cells appear as minute bodies, dark in colour, due to the air they contain.
Tissues. — If a transverse section of the stem of a Sun- flower be made and examined (see Fig. 87), the cells are seen to be arranged in a certain definite manner. On the outside a single layer of cells is arranged to form a covering to the stem. This covering forms the epidermis. In all cases the cells which cover the plant, and protect the deeper parts from injury, form the epidermal tissue. Within the section a number of groups of cells can be seen forming a nearly complete ring ; these are separated from the epidermis by a layer of cells. This ring of cells forms the vascular tissue of the plant. The separate groups of cells are called vascular bundles. In the centre, and between the vascular ring and the epidermis, a
F
66
BOTANY FOR BEGINNERS
CHAP.
number of cells can be seen. These fill up the interspaces, and can be called packing cells, or ground tissu^.
All the higher plants are built up of tissues. These tissues consist of cells which are grouped together to perform special work. The three kinds of tissues found in the section of the
stem of the Sun- flower are also found in leaves, roots, and flowers.
EXPT. 57.— If the ground under a Holly Tree be searched during autumn a number of leaves in va- rious stages of de- cay will be found. Some will be found with the soft material de cayed away, leaving a skeleton leaf. The veins of the leaf con- sist of very hard material, and have resisted the action of the atmosphere to a greater extent than the softer material which has
disappeared. The skeleton leaf consists of vascular tissue, as shown in Fig. 88, where a small quantity of the epidermis and ground tissue is shown near the apex of the leaf.
EXPT. 58.— Obtain an old Cabbage-stalk and cut a transverse section. Such a section is shown in Fig. 89, Examine it with the aid of a hand-lens, and note —
(i) The epidermis, this is shown at A, Fig. 89.
(ii) A ring of tissue is found between the centre of the stem, see B, Fig. 89, and the epidermis ; this is made up of vascular bundles.
(iii) In the centre a mass of tissue is found with a number of cavities in ; this is the pith. Between the epidermis and the vascular cylinder a ring of tissue can be seen, which is called the cortex. These cells form the ground tissue of the plant.
(iv) On the outside of the stalk is seen a number of marks.
FIG. 87.— Transverse section of stem of Sunflower A, epidermis ; B, cortex ; C, vascular ring, (x 7.)
HOW TO PREPARE AND EXAMINE SECTIONS 67
These are the places where the leaves were inserted ; they are called leaf scars (Fig. 89, D).
EXPT. 59. — Cut a transverse section of a twig of the Lime tree. Note — that the wood is made up of a number of rings. Each ring is made up of (a) a dark coloured layer and (b) a light coloured layer. These are shown in Fig. 90. Each ring represents the amount of growth which has taken place in one year. The age of the tree can be told by the number of rings of wood present
FIG.
3.— Skeleton leaf of Holly. (Half nat. size.)
FIG. 89.— A piece of Cabbage stalk. A= epidermis ; B = cortex ; C = vas- cular tissue ; D = leaf scar.
EXPT. 60. — Cut in autumn a longitudinal section of the stem of the Horse-Chestnut so as to pass through the base of a leaf. Examine such a section with a hand-lens. Note —
(i) The base of the leaf which is connected with the stem (see A, Fig. 91).
(ii) A layer of cork which consists of cells ; the layer passes right across (see B, Fig. 91) the base of the leaf. This layer, when the leaf has performed all its work, separates the leaf from the stem and covers up the scar which is left.
EXPT. 61. — Cut a transverse section of the stem of the Maize, and mount it in glycerine. If the stem has been preserved in alcohol so much the better, because there will be a smaller number of air bubbles present, and the section will be far clearer. Examine with the low power of the hand-lens. Note —
(i) The primary cortex. This surrounds the vascular bundles and helps to support the plant in an erect position.
V 2
68
BOTANY FOR BEGINNERS
CHAP.
(ii) The ground tissue which separates the vascular bundles, and in which they are embedded.
(iii) The vascular bundles which are scattered ; they are not arranged in the form of a ring as in the Sunflower. The bundles are smallest
and most numerous near the primary cortex, and largest and few in number near the centre of the stem.
All plants with scattered vascular
FIG. oo. — A piece of the stem 01 the Lime, showing annual rings.
FIG. oi. — Longitudinal section of stem of Horse-Chestnut. A, base of leaf; B, cork layer. ( X 3.)
bundles belong to the Monocotyledons, and those with the bundles arranged in a ring to the Dicotyledons.
FIG. 92. — Longitudinal section of stem of Sycamore, showing leaf fall and buds in the axils of leaves, (x 4.)
EXPT. 62. — Select an old root of the Maize from which a number of rootlets are growing. Cut transverse sections so as to pass through one of the young rootlets. Select one of the thinnest and mount in water or glycerine. Examine with a hand-lens. Note —
(i) The young rootlet which is found on one side of the section. (Fig. 93, R.)
vi HOW TO PREPARE AND EXAMINE SECTIONS 69
(ii) The way the rootlet springs from close up to the vascular bundles, and breaks through the cortex and epidermis.
EXPT. 63. — Dig up a few rhizomes of the Sweet Flag (Acorus). It can be found growing in ditches in Lancashire, Yorkshire, Somerset, Sussex, and in Scotland and Ireland.
Select a young one and cut transverse sections ; choose a thin section
and mount it in glycerine. Examine, and note —
(i) The scattered vascular bundles (Fig. 94).
(ii) The vascular cylinder formed by the numerous vascular bundles.
FIG. 93. — Transverse section of the root of Maize. R, R, roots. (Xi2.)
FIG. 94. — Transverse section of the rhizome of the Sweet Flag, (x 2.)
dr
s
(iii) A few roots which spring from close up to the vascular bundles may also be seen ; in Fig. 94 they can be seen breaking their way through the external tissues.
EXPT. 64. — From a stem of the Vegetable Marrow cut transverse sections. Select a thin one from these and mount it in water. Ex- amine and note —
(i) The pith (which may have dropped out).
(ii) The vascular bundles in which
ere are a number of large open essels.
(iii) The epidermis which presents a sinuous outline.
EXPT. 65. — Make a thin trans- verse section through the wood of the Pine which has been kept in FIG. alcohol for some time to remove the resin. Mount in glycerine, and examine. Note —
(i) The cells ; these are small and close together (Fig. 97) in one part of the section, but large in the remaining portion.
(ii) The small thick walled cells are formed in late summer and autumn,
95-— Tr >fVezeU
of Vegetable Marrow. The middle of section has dropped out. (X 5.)
;o
BOTANY FOR BEGINNERS
CHAP.
the larger ones in spring and early summer. The small cells are dark coloured ; these form the dark portion of the annual ring. The large cells are light coloured and form the lighter coloured portion of the annual ring.
EXPT. 66 — Cut a radial longitudinal section through a young stem of the Pine. Note—
(i) The cells are cut through lengthwise (Fig. 96), and some of them show a pitted arrangement.
(ii) A few fine lines will seem to cross the section in different parts ; these are the walls of cells which are cut across transversely.
EXPT. 67.— Prepare a transverse section of a young root of the Pine, which has been kept in spirits for some time. The root should not
FIG. 96.— Radial section of wood of Pins. (X5-)
FIG. 97. — Transverse sec- tion of wood of Pine. (X6.)
FIG. 98. — Transverse sec- tion of young root of Pine. (X 7.)
be above \ of an inch in diameter. Mount in glycerine. Examine with a hand-lens. Note —
(i) Around the outer part a series of cells which are arranged in regular rows ; these are cork cells, and form the protecting tissue of the root.
(ii) A number of annual rings which have the same appearance as those seen in the section of the stem of the Lime.
EXPT. 68. — Make a number of transverse sections through the stem of the Rose on which prickles are found. Select a thin section which passes through a prickle.
If this is examined by the aid of a hand-lens, the prickle will be seen to arise not only from the epidermis (Fig. 99), but also from a portion of the cortex.
EXPT. 69.— Obtain a leaf of the Rhododendron, and bleach it by- placing it in alcohol for a few hours. Cut a thin transverse section. This can be done by placing the leaf between slices of Potato, Carrot, or Elder pith. If a sharp razor be used, and slices be cut across the embedding substance so as to pass through the leaf, a number of sections will be obtained. Place these in water or alcohol in a watch glass, and
vi HOW TO PREPARE AND EXAMINE SECTIONS 71
pick out the thinnest. Mount in glycerine. Examine with the high power of the hand -lens. Note —
(i) The mid-rib, which is the most prominent part of the section. In the centre of this a vascular bundle will be seen, (ii) The epidermis which covers the whole surface of the leaf.
(iii) The ground tissue which comes between the lower epidermis and the upper.
How to Use a Compound Microscope —
The following is a set of rules to direct the student how to use the compound micro- scope : —
(1) Before commencing to use the micro- scope it must be examined to see if it is per- fectly clean. If any mounting media or reagents find their way on to the stage, clean them off at once with a soft clean cloth.
(2) To examine the lenses, the light must be directed up through the tube by the mirror. If the eye-piece be rotated, and specks of dust move with it, they are on the lenses of the eye-piece. The lenses must be unscrewed, and the dust cleaned off with a soft silk rag. If the
dust does not rotate with the eye-piece, it is on the objective, which must be cleaned in the same way. If either glycerine or Canada balsam is smeared on the objective, it must be cleaned by a jet of water directed on to it from a wash-bottle and then be carefully dried. Canada balsam is removed easily by alcohol or benzol.
(3) To examine a specimen on a slide — screw on the low power objective, and move the mirror until the whole field is illuminated.
FIG. 99. — Transverse section of stem and prickle of Dog Rose. (X 4.)
FIG. zoo.— Transverse section of leaf of Rhododendron. ( X 8.)
Then rack the tube down until it nearly touches the slide ; if the tube is now racked up very slowly the object will come dimly into view. In most cases a good view can be obtained with a low power without using the finer adjustment, but if there is any difficulty the fine adjust- ment can be used.
72 BOTANY FOR BEGINNERS CHAP.
With a high power the method of finding the focus is the same, only greater care is required. If the £ objective is used, it can be racked down until the image of the objective appears to meet the objective when the specimen is nearly in focus. If the tube is gently racked away from the slide it will come into view, and with the finer adjustment the focus can be found.
The pupil must on no account rack the tube towards the object at the same time he is looking down it. If this is done the object may be missed and the objective may be forced through the slide. The section may in this way be damaged and the lens ruined. The best way is to look at the objective until it is nearly close to the object, and then, while looking down the tube, rack it away until the object becomes clear.
(4) An object should always be examined with the low power first, and after all possible detail has been made out with this, the high power can be used.
(5) A high power must never be used unless the object is covered with a cover-glass. This prevents the mounting media from touching the objective.
(6) Drawings should always be made of the objects examined. This practice compels attention to details, and tends to produce the habit of close observation. In drawing, a fine pointed pencil should be used, and the drawings made either on good cartridge paper or Bristol board. The drawings should always be made to scale.
SUMMARY.
Sections of a plant can oe made in three directions. If the section of the stem is made at right angles to its long axis it is called a transverse section. When the section is made in the direction of the long axis of the stem and passes through the organic centre, it is a radial longi tudinal section. If the section passes lengthwise through the stem but does not pass through the organic centre, it is said to be a tangential longitudinal section.
Mounting Specimens. — Fresh specimens can be mounted in water, and material which has been preserved in alcohol must be mounted in either alcohol or glycerine. Sections must be kept wet to prevent air bubbles from forming. Cleanliness is necessary if good work is to be done.
Hand-Lens. — A hand-lens is a piece of glass which possesses the property of magnifying objects, and is mounted in wood, horn, or metal for protection and use. To use such a lens it is necessary to hold it close to the eye and to bring the object into such a position that it can best be seen.
Cells. — Plants are built up of elements which receive the name of cells. A cell is surrounded with a cell-wall, and contains protoplasm.
Tissues are formed by the union of a number of cells. There are three kinds of tissues ; they are- Epidermal tissue ; Vascular tissue ; Ground tissue.
vi HOW TO PREPARE AND EXAMINE SECTIONS 73
The Compound Microscope is an instrument which consists of lens and accessory parts. Such an instrument is used for the examination of the minute parts of plants.
QUESTIONS ON CHAPTER VI.
(1) What do you understand by the term " section''? What kinds of sections can be made from a stem ?
(2) Write a set of rules to guide you in mounting sections.
(3) Why, in mounting sections, must a cover-glass be placed over the object ; and how is such a cover glass put on ?
(4) Explain what is meant by air-bubbles, and how they find their way into sections.
(5) A hand-lens and a transparent section are given to you. How should the lens be used so as to examine the section?
(6) What is a cell ? Of what parts does a cell consist ?
(7) A Tomato is given to you to make a preparation showing the cells. Explain how you would proceed to do this.
(8) Explain what is meant by the term "tissue." What kinds of tissue can be found in plants ?
(9) Give an account of the structure of the stem of the Sunflower, and compare it with the stem of the Maize.
(10) Explain the term annual ring, as applied to woody trees. How- is it that each ring is formed of a light coloured layer and a dark coloured layer ?
CHAPTER VII
THE HISTOLOGY OF THE CELL
The Cell. — All parts of plants agree in being built up or microscopic elements which have received the name of cells (p. 65). The cells which are present in a woody plant, such as the Oak, may be living or dead. ^Head-cells perform an important func- tion in giving firmness and .rigidity to the plant. They may also conduct water from the roots to the leaves, and protect the deeper parts of the plant from injury. Cells may be separate, as in the ripe pulp of the Tomato, but in most cases they are united to form a tissue. Cells vary very much in form and development, and upon this will depend the kinds of tissue which they may produce. It will be an advantage to begin by studying the individual cell.
The Structure of a Cell.— As living cells change with age it will be better to take a young cell and to follow it until it
becomes mature. P In a young cell,
such as can be seen in the cortical (p. 66) tissue of the stem of most plants, the follow- ing three principal constituents can be distinguished. On the outside a mem- brane separates the cell from others which surround it, and is called a cell- wall. In close contact with the whole surface of the cell-wall, and filling the entire cavity of the cell, is the protoplasm. Embedded in the protoplasm is a . denser granular portion which is called the nucleus.
cw
FIG. 101. — The left-hand. figure, a young parenchyma cell; the right-hand figure, an older cell. CW, cell-wall ; P, Protoplasm ; N , nucleus ; N L, nucleolus ; V, vacuoles.
THE HISTOLOGY OF THE CELL
75
Formation and Growth of the Cell- Wall.— The cell- wall is very strong and elastic, and is formed from and by the proto- plasm, and its increase in thickness and area depends upon the vital activity of such protoplasm. The cell-wall may grow in area owing to the stretching caused by the pressure set up inside the cell, but throughout this increase -in size new material is deposited to strengthen it. In some cases the stretched cell- wall breaks, and the ruptured edges separate. The break is commonly repaired by the deposition of a plug of new material which connects the disconnected surfaces.
The cell-wall grows in thick- ness by the deposition of suc- cessive layers on the internal surface of the first-formed layer. This kind of growth is termed growth by apposition. The subsequent growth of the cell- wall by the deposition of new material between the old is called growth by intussuscep- tion. As a general rule growth in thickness does not take place
until after a cell has reached its full size. When such a cell-wall is examined "by the high power of the microscope, it exhibits a stratified appearance; this is owing to the constituent layers acting on the light differently. All the markings which are found on cell-walls are due to the unequal deposition of the new material during growth in thickness. The spiral, annular, and pitted walls, for example, which are found inThe wood of most plants, are caused by this unequal growth.
The Chemical Composition of the Cell Wall.— If a few cells be treated with iodine-stain 1 the cell-wall will assume a yellow colour, and the further addition of a single drop of
1 Iodine-stain is made by dissolving crystals of potassium iodide in distilled water until a strong solution is made and then adding crystals of iodine. If this is diluted with distilled water to the colour of brown sherry it is ready for use. The alcoholic solution is made in the same way, only alcohol is used instead of water.
FIG. 102.— Cell with thickened wall. in, middle lamella ; t, pit ; 7f , pitted transverse wall. ( X 300.) (S.)
76 BOTANY FOR BEGINNERS CHAP.
strong sulphuric acid causes the yellow colour to be replaced by a deep blue.
This reaction is characteristic of a substance termed cellulose. We may consequently conclude that the cell-wall consists principally of such cellulose. Cellulose consists of three chemical elements, known as carbon, hydrogen, and oxygen. All organic bodies which have the hydrogen and oxygen present in that proportion in which these elements are present to form water are grouped together as carbohydrates. The proportion by weight in which carbon, hydrogen, and oxygen are present in cellulose is represented by the following percentage composition : —
Carbon 44-44
Hydrogen . 6' 17
Oxygen 49'38
99.99 (= 100 very nearly.)
From this it will be seen that there is eight times as much oxygen as hydrogen by weight in cellulose.
But water is made up of eight parts by weight of oxygen to one of hydrogen, as the following analysis shows : —
Hydrogen 11*136
Oxygen 88*864
lOO'OOO
Hence, we are justified in classing cellulose as a 'carbo- hydrate.
Mineral substances such as silica, carbonate of lime, and compounds of iron are also found deposited in cell-walls.
Chemical Changes which the Cell-wall may under- go.— i. A portion, or all, of the cell-wall may become cuti- cularised. This is caused either by a change in the cellulose, or by the deposition of cutin in the cell-wall.
The epidermal cells of some leaves afford a good example of cuticularisation. If a section of a leaf of the Rhododendron be touched with iodine and sulphuric acid, some of the layers of the wall of the epidermal cells will assume a deep blue colour ; the colour is deepest in the inner layers, the outer layers not
vii THE HISTOLOGY OF THE CELL 77
showing it at all. The external layer of the epidermal cells is called cuticle, which is almost impermeable to water.
The walls of corky cells have the same properties as cuti- cularised cell-walls, and they give the same reaction with iodine. The corky walls consist of a substance called suberin. Both cutin and suberin contain about 74 per cent of Carbon.
2.— The cellulose of the cell-wall may, owing to the deposition of lignin in the wall, become lignified. A lignified wall gives a blue colour when treated with aniline chloride and hydro- chloric acid. Lignification, while it makes the cell-wall harder and more elastic, does not prevent water being able to readily traverse it. Lignification takes place most largely in woody tissue, and to a less extent in other parts of the plant.
3.— In some cases the cell-wall may become more or less mucilaginous. This change is caused by the conversion of cellulose into mucilage, which may be either a form of cellulose or a form of gum.
EXPT. 70. — Obtain a small quantity of Spirogyra, which is found in ditches and ponds during summer. Mount some of it in water, and examine it under a low power of the microscope. . Note —
(i) That the filament is surrounded by a cell-wall.
(ii) That each cell contains protoplasm.
(iii) That a nucleus is present in the protoplasm.
Place a small quantity of Spirogyra in a watch glass and cover it with iodine solution. Mount it in water and examine it first with a low power, then with a high power. Note —
(i) The cell-wall is but slightly stained yellow.
(ii) The protoplasm is coloured a deeper yellow or brown.
(iii) The nucleus is still more deeply stained than the protoplasm.
EXPT. 71. — Take a Date stone and scrape away the brown coat. Cut sections from the reserve material (which is cellulose) stored up in the seed. This can be done by using either the heel of the razor or a strong knife. Mount a thin section in glycerine, and examine first under a low power and then under a high power. Note —
(i) The thick cell-walls with a number of thin places called pits in them ; the membrane which closes those pits is called the closing membrane, and is, in reality, the primary cell- wall. For this reason the closing membrane is sometimes called the middle lamella (Fig. 102).
(ii) The granular protoplasm.
(iii) Soak a section for a few minutes in iodine, and mount in glycerine. The cell- wall is stained slightly yellow.
(iv) Mount another section which has been soaked in iodine and a drop of strong sulphuric acid. Examine it under a low power only. Observe how the cell-walls swell, lose their sharp outline, and assume
BOTANY FOR BEGINNERS
CHAP.
(See that no sulphuric acid finds its way on to the
a blue colour, microscope).
EXPT. 72. — Take some cotton wool and first soak it in alcohol for half an hour to drive out the air. Mount it in water. Examine it first under a low power, then under a high power. Note-^
(i) The twisted filaments, which consist of single cells.
(ii) The thick colourless cell-walls.
(iii) The remains of the protoplasm seen clinging to the interior of the cell-walls.
(iv) Treat a small quantity with iodine solution — the walls stain slightly yellow.
(v) Add a drop of strong sulphuric acid after the cover-glass has been removed, when a distinct blue colour will be seen.
Evidently cotton consists principally of cellulose.
FIG. 103. — Section of endosperm of Date. (X 400.)
FIG. 104. — Cotton fibres. '
FIG. 105. — Longi- tudinal section of a Match, showing pits.
EXPT. 73. — Cut sections from a cork and soak them in alcohol. Mount the thinnest in water and examine with the microscope. Observe : —
(i) The cell-walls, which have a clear outline. The cells have lost their contents.
(ii) Treat another section with iodine solution, the walls stain yellow.
(iii) Treat another section with iodine and sulphuric acid, the walls stain yellow or brown, not blue ; neither do they swell with sulphuric acid, but keep their outline.
EXPT. 74. — Cut sections from a wooden match and soak them in alcohol to remove the air bubbles. Mount a thin one in glycerine, and observe the cell-walls, which are seen to have a number of pits (Fig. 105).
(i) Treat a section with iodine ; it stains yellow.
(ii) Treat another section with iodine and sulphuric acid ; it swells and stains brown.
NOTE. — A cellulose wall can thus be distinguished from a lignified or a corky wall because it gives a blue colour with iodine and sulphuric
THE HISTOLOGY OF THE .CELL 79
acid. A lignified wall is stained brown and swells, and a corky wall is stained brown but does not swell.
EXPT. 75.— Soak some Linseed seeds in water, and note how they swell. The outer layers of the seed, which were hard and horny, have been converted into mucilage.
Make a section from a dry seed and mount in glycerine and water. Examine with a low power, and notice the wall swells and the striations on it become very clear.
The Protoplasm.— The protoplasm is the living and active part of the cell. It is a semi -solid material, which has embedded in it a number of granules, and is kept moist by the cell-sap, which saturates the wnole of the cell.
It is probable that the protoplasm consists of a number of fibres which cross in all directions to form a net-work, the meshes of which are filled in with a more fluid substance.
In living cells the protoplasm is always in close contact with the cell-wall ; but if the temperature of the cells be raised to 120° F, the protoplasm coagulates, i.e., sets like the white of an egg when boiled. In this state it loses all power of movement and dies. Alcohol or weak acids produce similar result.
The Composition of Protoplasm.— If a few cells are treated with iodine, the protoplasm is coloured brown. This is the same colour which the substances called proteids give with iodine, and it seems very probable that protoplasm is built up of proteids.
A proteid is a substance which contains Carbon. Hydrogen, Oxygen, Nitrogen, and Sulphur. The essential element of a proteid is nitrogen, and in some cases the name nitrogenous substance is used in place of proteid. The proportion of the above elements in living protoplasm is not known. If an analysis is made of protoplasm it is necessary to kill it in the process, and there may be a difference between the com- position of living and dead protoplasm. Protoplasm certainly contains the same elements which are found in proteids. It is the most wonder- ful substance in the universe, because life is never found apart from it. There appears to be no difference between the protoplasm of plants and that of animals.
The Movement of Protoplasm.— The protoplasm of a plant cell possesses the power of movement. These movements can be observed in large cells with thin and transparent walls, especially when the colourless protoplasm contains a large number of granules. These granules are driven backwards and forwards with the stream, and they appear much as particles of
8o BOTANY FOR BEGINNERS CHAP.
mud would do in a swiftly moving river. When the granules in their movements go round and round the interior of the cell, the movement is called rotation.
In an old cell where the protoplasm does not completely fill the interior of the cell the spaces are termed vacuoles. Vacuoles are filled with cell-sap. The connection between the protoplasm in different parts of the cell is kept up by strands of protoplasm. In such a cell the granules move up one strand and down another, much as the blood corpuscles move in the blood stream. This latter movement, which is more complex than that of rotation is called circulation. The indi- vidual granules in the current can be seen to move with unequal rapidity, according to their sizes, the smallest moving fastest.
The currents in the protoplasm are apparently irregular, now advancing, now retreating, sometimes suddenly arrested, and commencing again with increased rapidity. The movements depend upon temperature. In winter, during frost, and in summer, during dry weather, they are arrested. In spring, when there is plenty of moisture and a fair amount of heat, they are seen at their best.
EXPT. 76. — Obtain a plant of the American Water 'Weed (Elodea] and mount a single leaf in water. Place a cover-glass on, and examine wMi a high power. Note —
(i) The cells and the granules in the protoplasm.
(ii) The movement of the granules ; they move round and round— this is rotation.
(Hi) Gently"warm the slide over hot water. Examine again. The temperature being raised the granules move faster.
(iv) Now hold the slide either over a gas flame or a spirit lamp until the water boils. Examine again. There is no movement, the protoplasm has been killed.
EXPT. 77. — Remove a portion of the epidermis of a Stinging Nettle and mount it in water ; examine with the low power. Notice —
(i) The hairs ; focus one in the centre of the field and, using the high power, observe —
(ii) The cell is wider at the base than at the apex of the hair; examine the protoplasm, nucleus, vacuoles, and cell-wall.
(iii) The granules are seen in a state of motion ; they move up one of the strands and down another — this is circulation.
EXPT. 78. — Remove a small portion from near the core of an American Apple. Mount in water and examine under a low power ; fogus a cell
VII
THE HISTOLOGY OF THE CELL 81
near the centre of the field and proceed to observe a single cell with the high power. Make out —
(i) The cell-wall, protoplasm, nucleus, and vacuoles>
(ii) Treat with iodine solution ; the protoplasm is stained brown, and the nucleus a very dark brown.
(iii) Treat a freshly prepared specimen with salt solution (2\ per cent. ). The wall retains its original position and appearance, but the protoplasm contracts and leaves the walls. This is known as plasjnolysis.
(iv) Wash out the salt solution with water and 'exainlne again ; the protoplasm slowly regains its original position.
The contraction of the protoplasm is due to the salt solution attracting the water from the cell ; and it regains its original position when water again is taken in.
The Nucleus. — The nucleus is a denser portion of the proto- plasm ; it stains a deeper colour when treated with iodine solution. In shape the nucleus is somewhat oval, and in its interior a distinct rounded body called a nucleohts may be pre^ sent. It is built up of proteids, and contains a large quantity of phosphorus. A nucleus is present in all cells, and this seems to show that the presence of such a body is necessary to the life of the cell. It is always formed from a preceding nucleus. The exact function of the nucleus is not known, but in every case of cell-production the nucleus divides first. It has been suggested that the nucleus is the most important part of the cell, and that it forms the protoplasm which surrounds it.
The Difference between a Young and Mature Cell. — A very young cell is completely filled with protoplasm. As the cell increases in size the cell-wall grows faster than the protoplasm, causing cavities, which become filled with cell-sap, to appear in it. These cavities are called vacuoles, which in a very old cell may be very large.
The Contents of the Cell.— The cell always contains a number of other substances in addition to the protoplasm and the nucleus. In fact, at one time or another, it contains every element that the plant contains, for the puatoplasm is the active material of the cell, and produces all the organic substances found in the plant. The vacuoles and all parts of the cell are saturated with cell-sap. The protoplasm contains granules, which, according to their nature, are variously known as chloro- plasts, leucoplasts, and chromoplasts. Starch and Aleurone grains are also found in cells, while fats and, in some cases, crystals of calcium oxalate may be present.
G
82 BOTANY FOR BEGINNERS CHAP.
The Cell-Sap is the watery fluid which saturates the proto- plasm and the cell-wall, and also occupies the vacuoles ; it con- sists of water which holds in solution a number of organic and inorganic substances. The substances in solution are either on their way to be built up into protoplasm, or have themselves been formed by previously existing protoplasm. The organic substances present in cell-sap are sugar, organic acids, proteids, and in many cells colouring matter. The inorganic substances are chlorides and sulphates of potassium and sodium. Solid bodies, in addition to these dissolved substances, may also be present in the vacuole, e.g., starch grains, aleurone grains, and raphides or needle-like crystals of calcium oxalate.
Chloroplasts. — In the cells building up the green parts of plants a green colouring matter is present called chlorophyll. In all the higher plants the chlorophyll is found in the form of granules known by various names, as chlorophyll grains, chloro- phyll corpuscles, or chloroplasts. A chloroplast is a small mass of protcplasm saturated with chlorophyll. This is shown to be the case when a cell which contains chloroplasts is treated with alcohol. The chlorophyll is dissolved out, and colourless grains are left behind 7~these are called leucoplasts.
It is only in those cells which are exposed to light that chlorophyll is developed. The conditions necessary for the development of chlorophyll, are : —
(a) a certain temperature, a few degrees above the freezing point ;
(b] light ; any light will do if it is only intense enough ;
(t) a small quantity of iron in the food of the plant. The necessity of iron for the development of chlorophyll is very interesting, for no iron is found in the chlorophyll itself. The iron is probably necessary in the chemical changes which result in the formation of chlorophyll.
From what has been said about light being necessary for the formation of chlorophyll, it will be understood why it is found only in the surface cells. The important function of chlorophyll, which can only be exercised in the presence of light, is to absorb the carbon dioxide in the atmosphere, and to split it up into carbon and oxygen. The oxygen is returned to the air, but the carbon combines with the elements of water to form sugar
VII
THE HISTOLOGY OF THE CELL
which is eventually converted into starch. The starch grains are formed inside the chloroplasts.
Chloroplasts ultimately undergo decay, when, as in the case of frilling leaves, all that is left of them are a few yellow granules. During autumn the nutritive matters in the cells of the leaves are carried to other parts of the plant to be stored up for future
FIG. 106. — Epidermis from under side of a leaf of Iris, showing chloroplasts. A, surface view ; B, in transverse section ; s, stoma ; a, air cavity ; f, depression ; c, cuticle. (X 240.) (S.)
use ; and with these nutritive materials the greater part of the chloroplasts are removed. In the Copper Beech the chlorophyll is masked by colouring matter, which is dissolved in the cell-sap.
Leucoplasts. — In those cells not exposed to light, colourless granules are found ; these are called leucoplasts. Leucoplasts may IDC converted into chloroplasts if the cell in which they are present is exposed to light. The change of colour which a Potato may undergo when exposed to light is owing to some of
G 2
84
BOTANY FOR BEGINNERS
CHAP.
the leucoplasts being concerted into chloroplasts. The leuco- plasts perform the important work of converting sugar into starch. The starch grains are produced on the outside of the leucoplasts, not inside as in the chloroplasts. They are of
a denser consistency than chloroplasts, and somewhat flattened in shape. Qhr$mo- plasts are masses of proto- ptesm which are saturated with colouring matters other than chlorophyll.
FIG. 107.— Leucoplasts. A, C, D, E, viewed from side ; B, from above ; E, one changing colour. (X54O.) (S.J
FIG. 108. — Cells from pulp of Tomato, showing chromoplasts.
EXPT. 79. — Cut a thin section from a Beetroot, and mount it in water. Examine under a low power. Note —
(i) The large cells with their thin cell-walls.
(ii) The protoplasm which lines the cell-wall.
(iii) The coloured cell-sap which does not escape from uninjured cells.
(iv) Dip a fresh section in alcohol for half a minute, before examin- inc* it. The coloured sap oozes out because the protoplasm has been killed.
EXPT. 80. — Obtain a few Fern Prothalli from a gardener. Mount a small one in water, and examine with a low power. Note —
(i) The cells crowded with chlorophyll corpuscles.
(ii) Many of the chlorophyll corpuscles are undergoing division, as is shown by their shape. Grains shaped like an hour glass are under- going division.
(iii) Place a prothallus in a watch glass and cover with alcohol, and leave it for half an hour. Mount and examine. Note — The colouring matter has been dissolved out of the corpuscles, but they still retain their outline.
THE HISTOLOGY OF THE CELL
EXPT. 81. — Sow a few mustard seeds in two plant pots ; keep the soil moist ; place one in a dark place and the other in a light place. Observe from day to day. Note —
The stems and leaves of those plants kept in the dark are far longer than those grown in the light, but they are pale yellow or dirty white in colour.
Those grown in the light are bright green. Light is necessary for the de- velopment of chlorophyll,
EXPT. 82. — Obtain a few young Potatoes and cut them into slices. Place them in a weak solution of picric acid for a day or two. Wash the solution out with a weak solution of alcohol, and harden the slices in a 70 per cent, solu- tion of alcohol. Cut sections from near the surface, and stain them in alcohol and iodine solution. Mount in glycerine, and examine under a high power. Note—
(i) Some of the granules in the protoplasm stain blue. These are starch grains.
(ii) Attached to some of the starch grains small yellowish bodies may be seen ; these are leucoplasts.
Leucoplasts may be seen in colourless tissue in which starch is being stored up. Underground tubers and rhizomes contain them,
Starch Grains. — Chloroplasts in those cells which are exposed to light always contain starch grains. In many cases the starch grain is so large "that the chloroplast only
FIG. 109. — Cells from prothallus of Fern. (20.)
FIG. no. — Starch grains of Wheat. A, large ; B, small grains. (X54o.) (S.)
6
FIG. in. — Starch grains of' Oat?. A, compound grains ; B, isolated grains. (X540.) (S.)
surrounds it as a thin covering. Chloroplasts are always form- ing starch at the expense of the sugar which is produced by the constructive activity of the chlorophyll and the protoplasm. In the green parts of plants starch grains are very small because
86
BOTANY FOR BEGINNERS
CHAP.
they are always undergoing a change due to the action of a ferment found in the cells. This ferment, which is called diastase, reconverts the starch into sugar. Large starch grains are only found in those parts of plants where they are stored up for future use. Each plant produces a starch_grain which .differs in shape and size from the grains produced by other plants. By making use of this fact, adulterations of foods can be detected under the microscope.
Starch grains are always striated. The organic centre of the grain around which it grows by the deposition of new material is termed the hilum. The hilum is pro- duced by the activity of either the chloro- plast or the leucoplast, and the successive layers which are deposited are also due to the same activity. Starch grains grow in the same way that a cell-wall grows in thickness, that is, by apposition or by intussusception. In some cases compound grains may be found in cells. These can be divided into two kinds, (a) those called spurious, which are produced by two or more grains coming together and uniting as a result of pressure, (b) true compound grains which are produced by the same leucoplast, and round which there are always a number of layers which bind the grains together.
Starch grains can always be detected in
cells by treating them with iodine solution, when they give a deep-blue colour. They thus differ from cellulose which only gives a yellow colour with iodine.
Starch is a carbohydrate having the same composition as cellulose but differing in its physical properties. When treated with potash solution starch swells up, and if boiled with water will form a paste. If heated while dry, starch is converted into dextrine and becomes soluble.
Aleurone Grains.— Aleurone grains, or as they are some- times called, proteid grains, are found in many seeds. Each aleurone grain Is built up of a crystalloid and a globoid. The crystalloid is composed of albumen or proteids, and a
FIG. 112. — Starch grains from seed- leaves of Bean. (X 540.) (S.)
VII
THE HISTOLOGY OF THE CELL
FIG. 113. — A, cell from the endosperm of the Castor Oil plant ; B, aleurone grains ; g, glcboid ; k, crystalloid. (.X 540.) (S.)
globoid is formed of a double phosphate of lime and magnesia.
If a section of a Castor Oil seed be made and examined by the
high power of the
microscope, the
aleurone grains
will be seen to be
embedded in the
protoplasm, which
is also rich in oil.
The proteids are
stored up in plants
principally in the
form of aleurone
grains. They are
large in oily seeds
but small in starchy
seeds.
The crystalloids are sometimes found free. The crystalloids differ from mineral crys- tals because they swell up if treated with various re- agents.
Fats.— Drops of oil are found in the protoplasm in the cells of many plants. These drops are very nu- merous in the case of the seeds of the Castor Oil plant,
Rape, Flax, and in the fruit of the Olive. The non- nitrogenous substances stored up as reserve material in the above plants occur as drops of oil. When the seeds germinate the fat is converted into sugar.
Raphides. —In most plants crystals of calcium oxalate are
FIG. 114.— Section of grain of Wheat. /, pericarp ; /, seed coat ; al, aleurone grains ; am, starch grains ; n, cell nucleus.
BOTANY FOR BEGINNERS
CHAP.
found. They are always found in vacuoles, and when needle- shaped are called raphides. In many monocotyledonous plants they protect the plant from snails, slugs, &c.
Sugars. — Various kinds of sugars and allied bodies are found in the cell-sap. The principal forms of sugar thus found are grape-sugar and cane-sugar. Grape- sugar is found in the fruit of tile Grape, and Cane-sugar is found in the Sugar-cane and Beetroot.
EXPT. 83. — Scrape a freshly cut surface of a Potato tuber with a knife, and mount the scrapings in water. Examine first with a low power and afterwards with a high power. Note —
(i) The numerous starch grains which appear very bright. Observe the hilum and the stratified appearance of each grain.
(ii) Run some iodine solution under the cover- glass by holding a piece of blotting paper at one edge of it, and placing a drop of the solution on the other edge. The paper soaks up the water, and the solution takes its place. The iodine stains the starch grains blue.
(iii) Treat another preparation with chlor-zinc- iodine,1 which is an acid solution of iodine. The starch grains stain blue, but they also swell up and lose their bright appearance.
(iv) To a fresh preparation add potash solution. The grains swell.
EXPT. 84.— Cut a section from the Potato tuber and mount in water, examine with a high power and find
(i) A spurious compound grain, (ii) A true compound grain.
EXPT. 85. — Obtain a few Castor Oil seeds, and expose the pearly endosperm or reserve material by removing the outer covering. Cut a thin section of the endosperm and mount in olive oil. Examine with ths high power. Note —
(i) The aleurone grains or proteids granules, (ii) Find the crystalloid and globoid in the grain. EXPT. 86. — Cut sections from a cotyledon of the Almond, and mount in water.
Observe the bright-looking drops in the water ; they are oil drops.
1 Chlor-zinc-Iodine (Schulze's solution) consists of a mixture of zinc dissolved in pure hydrochloric acid, and a small quantity of potassium iodide dissolved in water. It is an acid solution of iodine.
Fii. 115.— Cell, with a bundle of Raphides. (X 160.) (S.)
VII
THE HISTOLOGY OF THE CELL
Formation of New Cells.— It is necessary that new cells should be produced so as to ensure growth and also to continue the life of the plant. The mode in which new cells are produced will depend upon the kinds of organs in which the
FIG. 117. — Diagram to illustrate cell division.
FIG. 1 16.— Starch grains from Potato. The left-hand figure shows a spurious compound grain ; the middle a true compound grain ; and the right-hand, figure ordinary starch grains.
division takes place. Cell-formation goes on in two different sets of organs, viz., vegetative and reproductive.
The vegetative parts of a plant are those portions which arc of service to the life of the individual, such as root, stem, branches and leaves. The method of cell-formation in all these organs is by simple division. In this case the nu- cleus first divides into two, the protoplasm then separates into two parts, and a cell- wall is formed between the newly formed nuclei. Two cells are thus formed. These cells are at first only half the size of the
parent cell, but they grow and become as large as the cell from which they were formed. In this method of cell formation there is only a portion of the cell-wall of the new cell which is new, the remaining portions belonging to the parent cell.
The reproductive parts of a plant are those portions which are concerned in the propagation of the species. They are a tax on the individual which bears them, for such individual must find the whole of the material necessary to give the off- spring a start in life. In all the higher plants this is done by the production of seeds, which produce new individuals, and so keep up the continuity of the species. Cell-formation in reproductive organs is characterised by a rounding off of the protoplasm : and no portion of the parent cell-wall aids in the formation of new daughter cells.
90 BOTANY FOR BEGINNERS CHAP.
The parent cell contains a nucleus, which, as before divides into two, and each part again divides, and thus there are four nuclei in the cell. The protoplasm now divides into four masses and each portion arranges itself around a nucleus. Each rounded portion of protoplasm produces a new cell-wall and the mother wall disappears, liberating the four cells. This method of cell formation is called free-cell formation, and it only takes place in reproductive organs.
SUMMARY
The Cell. — All parts of plants are built up of microscopic elements called cells, which may be living or dead. The Structure of a Cell. — Each living cell consists of —
(1) The cell-ivall, built up of cellulose.
(2) The protoplasm , which lines the cell-wall.
(3) The nucleus^ a denser portion of the protoplasm.
Changes which the Cell- wall undergoes. — It may become — (i) Cuticularised, (2) Lignified, (3) Mucilaginous.
Protoplasm. — The protoplasm is the living portion of the cell. It contains the elements carbon, hydrogen, oxygen, nitrogen, and sulphur. Protoplasm possesses the power of movement. It may rotate or circulate.
The Nucleus.— All cells possess a nucleus, and in it a mtclcolus may be present. It is built up of protoplasm, and contains a large quantity of phosphorus.
The Contents of the Cell. — The cell may contain —
Cell-sap. Starch grains.
Chloroplasts. Aleurone grains.
Leucoplasts. Chromoplasts.
Fats.
Crystals.
Chloroplasts are masses of protoplasm containing a green colouring matter called chlorophyll. The conditions necessary for the production of chlorophyll are —
1 i ) A certain intensity of light.
(2) A temperature above the freezing point.
(3) A small quantity of iron in the food. The functions of the Chloroplasts are —
1 i ) To absorb carbon dioxide from the air.
(2) To split up the carbon dioxide into carbon and oxygen.
(3) To form starch from sugar.
Leucoplasts are masses of colourless protoplasm. They form starch in those parts of the plants not exposed to light.
Chromoplasts are masses of protoplasm saturated with other colouring matter than chlorophyll.
Starch Grains are formed (i) by chloroplasts in organs exposed to
vii THE HISTOLOGY OF THE CELL 91
light, (2) by leucoplasts in the underground stems, roots, &c. Starch grains grow by apposition and intussusception.
The hilum forms the organic centre of the grain. Successive layers are deposited round the hilum, thus giving the grain a stratified appear- ance. A ferment (diastase) can convert starch into sugar. Starch grains may be simple, spuriously compound, or truly compound.
Composition of Starch. — It is built up of the same elements as cellulose. It is a carbohydrate.
Aleurone Grains. — The proteids found in plants are stored up as aleurone grains and proteid crystals. Each aleurone grain consists of a crystalloid and a globoid.
Formation of New Cells. — New cells are produced by (i) simple cell division, (2) free-cell formation. The former method takes place in vegetative organs, the latter in reproductive organs.
QUESTIONS ON CHAPTER VII
(1) Describe the structure of a young cell, and explain how it differs from a full-grown cell.
(2) How is the cell-wall formed, and how does it grow in thickness ?
(3) To what are the markings due which can be found in cell-walls?
(4) Give an account of the composition and properties of cellulose.
(5) Describe the structure of a living parenchymatous plant cell. What chemical elements enter into the composition (a) of the cell-wall, (b) of the protoplasm ?
(6) How can you distinguish by the aid of the microscope a cellulose wall from (a) a lignified wall, (b) a corky wall, (c) a mucilaginous wall?
(7) What is protoplasm ? What do you know about the properties of protoplasm ?
(8) What is meant by the circulation of protoplasm?
(9) Enumerate and give a brief account of the most important sub- stances which are found in cells.
(10) What is a chloroplast ? Where are chloroplasts found? What work can they perform which makes them useful to the plant ?
(n) Give an account of the conditions which are necessary for the development of chlorophyll.
(12) What is a leucoplast? How may a leucoplast be converted into a chloroplast ? Why are leucoplasts said to be starch builders ?
(13) What is the nature of starch? How is it formed, and what are its uses ?
(14) To what substance do the green parts of plants owe their colour ? State and explain the nature of the work which green parts of plants are alone able to perform.
(15) What is an aleurone grain ? Where are aleurone grains found ?
(16) How are new cells formed ? What kinds of cell-formations are there ?
(17) Explain clearly how starch is formed in a Potato, and from what source it is derived. (1899.)
CHAPTER VIII
THE HISTOLOGY OF THE TISSUES
Kinds of Cells.— All cells can be classed according to their shape into (a) Parenchyma, and (b) Prosenchyma.
A parenchyma cell is one in which the diameter of the cell is about the same in every direction. Cells of this description are especially abundant in the succu- lent parts of plants. The ground tissue of a plant is composed of parenchyma cells, and in many cases they form a storehouse for reserve material, as in the turnip. When such cells are very numerous in an organ they are said to form parenchymatous tissue.
A prosenchyma cell is long and nar- row. Cells of this description may lose their living contents
and become filled with air and water. If a number of prosenchyma cells are placed end-to- end so that the transverse walls are at right angles to the long side walls, the transverse walls may become perforated, and so form a vessel. The living contents of the cells be- come absorbed after the transverse walls are broken down, and eventually the fully formed vessels contain only air or water. The markings on the walls of the vessels supply the botanist with their characteristic names.
FIG. 118. — Parenchyma cell from fruit of Bean. ( X 500.)
FIG. no.— Dia- gram of Prosen- chyma cell.
CH. vin THE HISTOLOGY OF THE TISSUES
93
20. — Pitted, spiral, annular, and reticulate vessels.
If the walls are pitted (p. 78) they are called pitted- vessels. When the thickenings of the walls appear to form a spiral, the vessels are spoken of as spiral (Fig. 120). When the markings give to the vessel a reticulate or netted appearance, such vessels are termed reticulate (Fig. 120). If the transverse walls have been per- forated by a single round opening while the rest of the walls remain to form thick rings the vessels are called annular. Vessels of the above kinds are found in the wood p,G> of all plants. The walls of all such vessels are lignified.
Sieve Tubes. — In the formation of the sieve vessels or sieve tubes the transverse walls are not completely broken down, but they are perforated by fine canals through which the protoplasm passes — for such vessels keep their living contents.
The wall which contains the perforations is called a sieve plate. In some plants the longitudinal walls may become simi- larly perforated so that sieve plates are also formed there. The walls of sieve tubes are always unlignified, and the ves- sels contain a watery cell- sap. In close contact with the sieve tubes, and formed from the same cells during development, long narrow cells are
formed, and these are called companion cells. The nuclei of the sieve tubes are broken up and disappear, but the com- panion cells keep both their protoplasm and nuclei.
Kinds of Tissues. — When a number of cells are intimately connected, and perform the same kinds of work, they are
FIG. 121. — Parts of sieve tubes from Vegetable Marrow. A, surface view of sieve plate ; B, C, longitudinal sections, showing sieve plates ; D, contents of sieve tube ; S, com- panion cells ; PA, protoplasm ; C, lateral sieve plate. (X 270.) (After Strasburger.)
94
BOTANY FOR BEGINNERS
CHAP.
spoken of as forming a tissue. In the higher plants there are three kinds of tissue systems, they are called epidermal tissue, vascular tissue, and ground tissue. The above tissues may be primary or secondary. Primary tissues are formed from the growing cells of the embryo, and the secondary tissues from those new layers of growing cells which are formed from the embryonic cells.
EPIDERMAL TISSUE
Epidermal Tissue.— Those cells which cover the plant and protect the deeper parts from injury, form the epidermis.
FIG. 122. — Surface view of the epidermis from FIG. 123. — Surface view of the underside of leaf of Balsam, showing stomata. epidermis of the Dog's
(X 160.) (S.) Mercury. (X 300.) (S.)
As a rule the epidermis is only one cell in thickness, and the cells do not contain any chlorophyll. The protoplasm of the epidermal cells is reduced to a very thin layer which lines the cell-walls, and the cavities of the cells contain a colourless cell- sap. The outer wall of the epidermal cells forms a cuticle, which protects the deeper tissue from a too rapid loss of water.
Stomata are found in the epidermis of all those parts of plants which are exposed to the air. Each stoma is a minute opening between two cells which contain chlorophyll and are called guard-cells. The stoma is formed by a young epider- mal cell becoming divided by a septum into two equal cells.
VIII
THE HISTOLOGY OF THE TISSUES
95
FIG. 124. — Diagram illustrating formation of stoma. i, young epidermal cell ; 2, division of cell ; 3, the cell-wall split to form the stoma.
The septum then splits open, the opening constitutes the stoma,
and the cells form the guard-cells. The size of the stoma
depends upon the movement of the guard-cells. The stomata
are found on all the green parts of plants, but they are most
numerous on the under side of the leaves. If both sides of a leaf are alike, the stomata will be equally developed on both the upper and lower surfaces. In those plants with floating leaves the stomata are found on the upper side only. Stomata can open and shut by the change in the shape of the
guard-cells. The interchange of gases between the interior of
the plant and the external atmosphere — froin which interchange
the plant obtains energy and food material — goes on through
the stomata, which also give out watery vapour.
Some plants have openings in the epidermis by which they
give out water in a liquid state. Such openings are called
w a t e r-p ores.
The water - pores
are larger than the
stomata and are
always open. Hairs. — From
the epidermis hairs
are produced (a) for
protection (b} for
the nutrition of the
plant. When the
hair consists of a
single cell it is said
to be unicellular ;
if a number of cells
enter into the com- position of a single
hair it is termed
a multicellular
hair. The former are found on the roots of plants, where
they take in water containing minerals in solution. The latter
FIG. 125.— Waterpore, with a portion of epidermis from a leaf. (X 240.) (S.)
BOTANY FOR BEGINNERS
CHAP.
are found on the stem, leaves, and flowers of most plants.
The unicellular root -hair is produced by the outgrowth of an
epidermal cell.
On the surface of the stinging nettle a very large number of
hairs are produced. If one is examined by the microscope it is
seen to consist of a single cell at the apex ; the base of this cell is fixed in a number of cells which be- long to the epidermis. The tip of the hair of a stinging nettle is strengthened with silica, while the rest of the hair con- tains carbonate of lime. In the ter- minal cell a poisonous fluid is produced. When an animal touches the plant the stiff pointed hairs enter its skin and the poisonous fluid is poured into the wound. The well known smarting sensation which a person feels when "nettled" is due to this acid fluid. The well known method of rubbing the wound with a Dock leaf is to neutralise the acid with the alkaline secretion present in the Dock leaf.
Emergences. — Emergences are modified portions of the epidermis which may act as glands. A gland is an organ which secretes some sub- stance from the materials which are brought to it in the cell sap. The ten- tacles of the Sundew are well known examples. These secrete a substance very much like the gastric juice of the higher animals, and this secretion en- ables the plant to digest any insects which the plant may catch.
EXPT. 87.— Cut sections from a Turnip or from a Potato ; mount the thinnest in water. Note—
(i) The shape of the cells. They are parenchyma cells.
(ii) The contents of the cells. These consist principally of protoplasm and starch grains.
FIG. 126.— Stinging hair cf Nettle. (X6o.) (S.)
vin THE HISTOLOGY OF THE TISSUES 97
EXPT. 88. — Obtain either the stem of the Pumpkin or of the Cucumber ; harden in alcohol. Cut either radial or tangential longi- tudinal sections. Stain in iodine solution, and mount a few in glycerine. Note —
(i) The sieve tubes, the transverse walls of which are clearly seen owing to the substance which surrounds them being stained dark brown, the wall only staining faintly yellow.
The substance which surrounds the sieve plates is called callus, and it is probably com- posed of cellulose. The amount of callus present will depend upon the age of the sieve tubes, and the season of the year.
(ii) The protoplasm which lines the tubes and is well developed just over the sieve- plates.
(iii) The shape of the sieve tubes.
(iv) The companion cells. These are long and narrow and their nuclei can be clearly seen under the high power.
EXPT. 89. — From the lower side of the leaf of the Wallflower pull off a small portion of the epidermis ; this can be done by raising the epidermis with a knife and gently pulling at it ; as a rule the edge of the piece of epidermis will be thin enough for examination. Mount in water, and examine it with the high power. Note —
(i) The sinuous outline of the cell-wall.
(ii) The spindle-shaped hairs which lie close to the surface of the leaf.
(iii) The stomata, which are very numerous. Each stoma is surrounded by a pair of sausage- shaped cells — the guard-cells.
EXPT. 90.— Strip from the underside of the FlG 127._Digestive leaf of the Hyacinth (the leaf of any mono- gland of the Sun-
cotyledonous plant will do as well) a small dew- (x6o.) (S.)
portion of the epidermis. Mount in water and examine first under a low power, then with the high power. Note —
(i) The epidermal cells.
(ii) The stomata, which are very large and numerous.
Strip from the upper surface of the leaf a piece of epidermis and treat in the same way.
(iii) Compare its appearance with the lower epidermis and note in what ways they agree and how they differ.
EXPT. 91. — Mount in water the rootof a germinating Mustard Seed ; examine it under a low power. Note —
(i) The root-hairs ; these are unicellular, and are formed by the out- growth of the cells of the apidermis.
H
98 BOTANY FOR BEGINNERS CHAP.
(ii) To some of the root-hairs particles of soil adhere. This adhesion of the root-hairs to particles of soil is due to the con- version of the outer layer of the cell-walls into mucilage.
EXPT. 92. — Pull off a small piece of the epidermis of a leaf of the Sunflower ; mount in water, and examine under a low power. Note —
The multicellular hairs which are scattered over the surface of the leaf.
VASCULAR TISSUE.
Vascular tissue.— If a skeleton leaf be examined it will be found to consist of a number of hard fibres ; these are the vas- cular bundles. These bundles form the conductive tissue of the plant, that is, they conduct water from the roots up the stem, to the leaves, and the elaborated sap from the leaves to those parts of the plant which need it. Such bundles are also the principal supporting tissue of the plant and form the frame- work upon which the softer parts are fixed. The bundles always resist decay longer than the other parts of the plant, and in a skeleton leaf or stem are the only parts present. In the higher plants there are two principal types of vascular bundles, they are known as open and closed bundles. Open bundles are found in Dicotyledonous plants and closed bundles in Monocotyledonous plants.
Structure of Bundles. — If a vascular bundle of the Dicotyledonous type be examined under the microscope, there will be seen : —
(1) The Xylem, which is nearest the centre of the plant.
(2) The Phloem, which is always the portion of the bundle most removed from the centre of the plant.
(3) The Cambium, which lies between the xylem and phloem.
Xylem. — The xylem is the woody portion of the bundle, and in the vascular bundle of the stem it is always found nearest to the pith. It consists of a number of vessels and parenchyma cells. The vessels which are- found in the xylem are spiral (p. 93), annular (p. 93), reticulated (p. 93), and pitted (p. 93). The spiral vessels are the nearest to the pith, then come the annular vessels, and these two kinds together make up the first-formed xylem, called protoxylem. The reticulate vessels come next, and the pitted vessels are to be found close up to the Cambium. Scattered about among the vessels, fibrous cells are to be found. These fibrous cells are long and narrow, and in
vin THE HISTOLOGY OF THE TISSUES 99
some cases have sharp-pointed ends. Prosenchyma cells are also found mixed up with the vessels (p. 92).
In addition to the vessels and the fibrous cells a number of parenchyma cells occur mixed with the vessels ; these paren- chyma cells never fuse together.
Phloem. — The phloem consists of two portions which are known as the soft- and hard-bast. The soft bast is found close to the cambium and consists of sieve tubes, companion cells, and parenchyma cells. The sieve tubes (p. 93) are long vessels which have their transverse walls perforated. Com- panion cells — which can always be recognised in a longitudinal section of the bast because they are long narrow cells rilled with protoplasm, and each possessing a large nucleus — are found with the sieve-tubes. In transverse sections companion cells appear as if they were originally cut off from the same cells as the sieve-tubes. Mixed up with the sieve-tubes and com- panion cells a few parenchyma cells may be found ; these are known as phloem parenchyma.
The hard bast is composed principally of bast fibres, which are long narrow spindle-shaped fibres, much like the fibres of wood. Parenchyma cells are to be found mixed with the bast fibres.
Cambium. — The cambium is found between the xylem and phloem. It consists of cells which do not as yet show the characters of either xylem or phloem. Those cambium cells nearest to the phloem pass gradually into it, while those nearest the xylem eventually become the xylem. The cells near the middle of the cambium are thin walled, and contain protoplasm. They are in a state of constant division, and thus form new cells. The new cells on one side pass into and form new xylem. Similarly, on the other side new phloem is produced. A tissue composed of cells which can divide in this way is called meristematic, because it is capable of dividing up and producing new cells.
Open and Closed Vascular Bundles.— Those vascular bundles which possess a cambium are said to be open because they can produce new tissue. If the bundles consist of xylem and phloem only, without a cambium, they are termed closed bundles, because growth in thickness of the bundle cannot go on. When the xylem and phloem are in contact on one side only, they are said to be collateral.
H 2
100
BOTANY FOR BEGINNERS
CHAP.
The general arrangement of the elements in an open vascular bundle is shown below in a tabular form.
Near Pith.
Reticulate vessels Pitted vessels . .
Cambium cells. .
Sieve-tubes Companion cells
Bast fibres
I | Soft bast . Hard bast.
Xylem
Cambium
Phloem.
An
Open Vascular Bundle.
Bundle Sheath (PericycJe. )
The Monocotyledonous Type of Vascular Bundle.— If a vascular bundle of a monocotyledonous plant be examined, there will be found two kinds of tissue present. They are :—
(1) The Xylem, which always points towards the centre of the stem.
(2) The Phloem, which is turned towards the exterior of the stem.
The structure of such a vascular bundle is much the same as in the dicotyledonous type, only the variety of vessels is not so great. The bundle is surrounded by a special sheath of thick walled cells.
The Course of Vascular Bundles.— If the bundle passes from the stem into the leaf, as most bundles do, it is called a common bundle, because it is common to both stem and leaf. The portion of the bundle in the leaf is termed a leaf- trace. In a few cases the bundle never passes from the stem, and it is then spoken of as a cauline bundle.
The arrangement of the bundles in the stem depends upon the phyllotaxis (p. 36). If the arrangement of the leaves is |, the bundle which proceeds from the leaf will pass through five internodes before it joins on to the bundle below, as in the Wallflower.
If the leaves are decussate there will be four rows of leaves on the stem, and the bundle from any leaf will have to pass through two internodes only before it joins on to the bundle of the leaf below. Thus, the bundle which proceeds from a leaf will pass inwards for a short distance, then bend and pass down
viii THE HISTOLOGY OF THE TISSUES 101
the stem until it joins on to the bundle below. The above are the arrangements in most dicotyledonous plants.
The course of the bundles in monocotyledonous plants is very irregular. The bundles from any leaf base pass into the stem towards the centre, then bend back and pass for some distance down the stem, when they join on to the bundles below.
EXPT. 93. — Obtain a piece of the stem of the Wallflower with a number of leaves on it, and trace out the course of the vascular bundles. To do this bisect it longitudinally so as to pass through the middle of a leaf ; clear away the pith with a blunt knife. Note —
(i) That the bundle which enters the stem from the midrib of the leaf runs inwards for a short distance, then turns straight downwards, and ioins on to the leaf vertically below the first leaf.
(ii) That the bundle runs through five internodes without joining a bundle.
(iii) That there are two smaller bundles that act in the same way.
(iv) That in any section of the stem of the Wallflower there must be five large bundles and ten small bundles cut through.
EXPT. 94.— Trace the course of the vascular bundles in the stem of the Deadnettle. Bisect the stem longitudinally, so as to pass through two leaves on the same side of the stem. Clear the pith away, and note —
(i) That the bundle which enters the stem runs inwards and then downwards, and joins on to the bundle of the leaf vertically below.
(ii) That the bundle only passes through two internodes before it joins on to the bundle below.
(iii) That in the stem of the Deadnettle there are four main vascular bundles, which correspond to the decussate arrangement of the leaves.
THE GROUND TISSUE.
The Ground Tissue.— The tissue which is found in the centre of a stem and between the vascular bundles and the epidermis is called ground or fundamental tissue. It usually forms the principal part of the primary tissue of the plant, and can be arranged in three groups : —
The Pith within the ring of vascular tissue.
The Cortex between the ring of bundles and the epidermis.
The Medullary rays between the pairs of bundles.
The vascular bundles seem to be fixed in the ground tissue, which in a young stem appears to surround them. It may contain chlorophyll and be used for obtaining food.
While the epidermal tissue protects the internal parts of the plant and the vascular bundles perform the office of conduction and support, the ground tissue provides for the nutrition of the plant and forms a store for reserve material.
102 BOTANY FOR BEGINNERS CHAP, vin
SUMMARY.
Parenchyma cells are those in which the diameter is about the same in all directions.
Prosenchyma cells are long and narrow.
Vessels are formed by the perforation of the transverse walls of cells which are placed end to end. The following are very common : — Spiral vessels. Reticulate vessels.
Annular vessels. Pitted vessels.
Sieve tubes are formed from cells which have their transverse walls perforated to form sieve plates.
Tissues. — There are three tissue systems in a plant, viz. : —
Epidermal tissue, which covers and protects the deeper parts of
the plant from injury. Vascular tissue, which forms the supporting and conducting tissue
of the plant. Ground tissue, which fills in the spaces between the epidermal and
vascular tissue.
Stomata are the small openings which are found between guard -cells in the epidermis of the aerial parts of plants.
Hairs may be either unicellular or multicellular. They may protect the plant from insect pests, or be used for taking in food.
Vascular bundles may be closed or open. If the bundle is open it will consist of ( I ) Xylem ; (2) Cambium ; (3) Phloem.
If the bundle is closed it will consist of (i) Xylem, and (2) Phloem. The Course of Vascular Bundles depends upon the arrangement of the leaves on the stem.
QUESTIONS ON CHAPTER VIII.
1 i ) How does a parenchyma cell differ from a prosenchyma cell ?
(2) What is a vessel? How are vessels formed? Enumerate the different kinds which are found in wood.
(3) In what respects of structure and function do the vessels of the bast (sieve tubes) differ from those of the wood ? (1892.)
(4) Describe fully the structure of a vascular bundle in the stem of a dicotyledon. Explain how such a bundle differs from that of a mono.- cotyledon. (1894.)
(5) What is a stoma? On what parts of the plant are the stomata chiefly developed ? How is a stoma formed ?
(6) Give an account of the structure of the epidermis of a leat.
(7) What is a vascular bundle ? Of what parts does it consist ? (1898. )
(8) What is the cambium ? Explain where you would find it in the trunk of a tree, and what its importance is? (1898.)
(9) Describe the structure of a young parenchyma cell, and explain how it differs from that of a full-grown cell of the same kind. (1892.)
(10) Explain what is meant by ground tissue. In what parts of a plant is ground tissue found ?
(u) Give a short account of the longitudinal course of the vascular bundle in a dicotyledonous plant.
(12) What kinds of hairs are found on plants? Of what use to the plant are hairs ?
CHAPTER IX
THE HISTOLOGY OF THE SHOOT AND ROOT
The Structure of a Dicotyledonous Stem.— A trans- verse section of a young dicotyledonous stem, when examined under the low power of the microscope, shows the follow- ing parts (Fig. 128). Exter- nally the section is limited by a single layer of cells, many of which may produce hairs ; this is the epidermis. Inside the epidermis comes the cor- tex, bounded on the inside by a single row of cells called the endodefmis. Inside the endodermis a broken ring of vascular bundles is found, which is surrounded on the outside by a layer of cells,
known as the pericycle/ The vascular bundles are divided from one another by a number of cells forming medullary rays. The centre of the stem is full of loose cells which form the pith.
FIG. 128. — Transverse section of young stem of Sunflower, showing ten sepa- rate vascular bundles in the ground tissues. Ef>, epidermis ; co, cortex ; Pi, pith ; Pit, phloem ; cb, cambium ; xy, xylem.
Outside. Epidermis . Cortex . . \ Endodermis j Pericycle . \ Phloem . . \ Cambium . I Xylem . . I Pith ....
Inside.
Epidermal Tissue Ground Tissue .
Vascular Tissue Ground Tissue
Transverse Section of Dicotyledonous Stem.
104
BOTANY FOR BEGINNERS
CHAP.
In an old stem of the Sunflower the vascular bundles form a complete ring, and in such an old stem a complete ring of cam- bium passes through the bundles and across the medullary rays. Those parts of this cambium ring which lie between the vascular bundles are spoken of as forming the interfascicular cambium (p. 99). The interfascicular cambium is formed by the cells between the bundles be- coming meristematic, i.e., they begin to divide up and so complete the ring. This portion of the cambium ring forms
FIG. 129. — Transverse section of older stem of Sun- flower, showing the first formation of interfascicular cambium. Ph. and cb, phloem and cambium ; xy> xylem ; Scl, sclerenchyma ; s, spiral vessels ; sf, interfascicular cambium.
FIG. 130. — Transverse sec- tion of part of cylinder of old Sunflower stem ; Ph, phloem ; cb, cambium ; xy, xylem ; WF, wood fibres ; MR, medullary rays \v, vessels of xylem.
vascular elements which partly fill up the spaces between the bundles. The whole of the cambium during the active period of growth produces xylem on one side and phloem on the other. Thus, in an old stem the vascular cylinder is formed (p. 66).
EXPT. 95.— Cut transverse sections of a young stem of the Wallflower and mount in water. Look for a thin section, and note —
(i) The epidermis, a single row of cells which surrounds the cortex.
(ii) The cut ends of the vascular bundles.
(iii) The ground tissue forming the cortex and pith.
ix THE HISTOLOGY OF THE SHOOT AND ROOT 105
EXPT. 96. — Transfer the thinnest section observed in Expt. 95 to alcohol, and let it remain for twenty minutes to bleach it. Now stain it with iodine solution, mount in glycerine, and examine a vascular bundle under the high power. Note —
(i) The endodermis, a single layer of cells containing starch. The starch grains stain blue.
(ii) The pericycle, a layer of cells inside the endodmeris.
-xy.
Fi
FIG. 131. — Diagram of old stem of Sunflower as seen in transverse section, showing an almost complete cylinder of secondary tissues, interrupted by medullary rays. (x 6.) Ep, epidermis \ co, cortex; Scl, sclerenchyma patches; Ph, phloem; cb, cambium ; jry, xylem ; Pi, pith.
(iii) The phloem inside the pericycle ; the transverse walls of the sieve tubes will be stained yellow, and the perforations through which the strands of protoplasm pass may be stained brown.
(iv) The cambium, several layers of cells inside the phloem.
(v) The xylem between the cambium and pith. This can be easily recognised by the large cavities of the vessels.
(vi) The pith, which fills the interior of the stem.
EXPT. 97. — Select a very young stem of the Sunflower. This can be obtained by germinating seeds, and planting out the young plants in plant pots. The stem should not be more than £th of an inch in
106 BOTANY FOR BEGINNERS CHAP.
diameter. Cut transverse sections and mount in water. Examine under a low power. Note —
(i) The epidermis.
(ii) The cortex.
(iii) The vascular bundles, which are not united.
(iv) The ground tissue between the bundles.
(v) The cambium, between the phloem and xylein.
EXPT. 98. — Cut transverse sections from a stem of the Sunflower, which is twice the age of the stem used in Expt. 97, and mount in glycerine. Observe — (i) The vascular bundles, (ii) The cambium ; see if a complete ring is formed.
EXPT. 99. — Prepare a thin transverse section from the stem of a full-grown Sun- flower, which has been kept in spirit for some time to remove the resin and air, and to harden the tissues. Mount in rb glycerine or glycerine jelly. Examine under a low power, and note —
(i) The vascular cylinder, which is formed by the union of the bundles.
FIG. 132.— Transverse section (ii) The pith, the cells of which have of young stem of Wallflower. lost their living contents.
vtsculafbundles^C^coAet; («*) The large multicellular hairs which E, epidermis ; A, hair. project from the epidermis.
EXPT. ioo. — Cut a radial longitudinal
section of the stem of the Wallflower, and mount in water. Examine first under a low power then under a high power, and note —
(i) The epidermis. (v) The phloem.
(ii) The cortex. (vi) The cambium,
(iii) The endodermis. (vii) The xyleni.
(iv) The pericycle. (viii) The pith.
Growth in thickness of a Dicotyledonous Stem.— In those perennial plants which possess open vascular bundles new additions are made to both the xylem and the phloem by the cambium which is between them. The xylem increases in size by additions to its outer surface, the phloem by additions to its inner surface, the central portion of the cambium remaining meristematic. Thus, every season new layers are produced, but far more xylem is formed than phloem. The rings which are seen in a cross section of the oak are produced
IX THE HISTOLOGY OF THE SHOOT AND ROOT 107
by the action of the cambium and each ring marks a years growth.
Each annual ring consists of a dark coloured layer and a light coloured layer. In spring, . when the active period of growth commences, the pressure on the cambium is very little, because during the winter the bark and cortex have been ruptured by the action of frost and changes in temperature. The cambium is able to produce large cells and vessels which are thin- walled, thus a light coloured layer is formed. During spring the ruptures in the bark are re- paired, and as the season advances, more and more pressure is brought to bear on the cam- bium, and smaller and thick - walled cells and vessels are formed. These are dark in colour because they con- tain less air, and thus a dark colour- ed layer is formed. The age of a tree
can be told by its annual rings, and if the rings are examined and compared the size of the layers will give us some clue to the kind of season when any ring was produced.
The Formation of Periderm.— In those plants which grow in thickness the epidermis is replaced by a new tissue which receives the name of periderm. The periderm is formed from the pericycle, which divides up into a number of rows of cells ; one of these rows forms the phellogen or cork cambium. The phellogen produces new cells on both its inner and outer surfaces ; the cells on the inside keep their living contents and form the phelloderm ; those on the outside lose their living contents and their cellulose walls are converted into cork. The cork cells are impervious to water, and so cut off the supply of water to the cortex and epidermis ; these con-
FIG. 133. — Section of Larch stem ; showing annual rings.
io8
BOTANY FOR BEGINNERS
CHAP.
sequently dry up and aid in the formation of bark. The parts which form bark and periderm are shown below : —
{Phelloderm Phellogen Cork cells
Bark.
Cork cells Endodermis Cortex Epidermis
The primary phellogen after a time ceases its activity, and a deeper phellogen is formed. Still later, even this may discontinue
FIG. 134. — Transverse section through stem of Maple. D, dried up epi- dermis and cortex ; C, 'cork cells ; PH, phloem ; XY, xylem. (X 150.)
FIG. 135.— L, Lenticel from the stem of the Lilac. (X25«) PD, phellogen ; PL, phelloderm ; E, epidermis.
its function, until at last the new phellogens which are produced come to be formed in secondary bast. If the bark which is produced by these deeper phellogens is thrown off in scales it is called Scaly bark ; this is found on the Pine and Plane tree. On the other hand, if the secondary bark forms complete rings which are concentric — ringed bark is formed, as in the Honeysuckle, Clematis, and Grape-vine.
Lenticels. — In the Periderm are produced small _ pores called lenticels. They are developed just beneath those places where the stomata existed in the epidermis. They are openings formed by the phellogen, which produces cells between which intercellular spaces are formed (Fig. 135).
EXPT. 101. — Prepare sections of the flower stem of the White Lily, and if the stem is fresh, mount the thinnest section in water ; if the material has been in spirit, mount in glycerine. Observe —
(i) The epidermis, a single layer of cells.
IX THE HISTOLOGY OF THE SHOOT AND ROOT 109
(ii) The cortex, which is several layers of cells in thickness, (iii) The pericycle, which is very strong and forms a thick ring, (iv) The scattered vascular bundles, which are embedded in the ground tissue.
EXPT. 102.— Cut a transverse section of a two-year-old stem of the Wallflower. Mount in water, and examine under a low power. Note—
(i) The periderm, which is formed from the pericycle.
(ii) The bark, which is outside the phellogen or cork cambium.
The Structure of a Monocotyledonous Stem.— If a transverse section of a young stem of the Maize be made and examined by a low power the following parts will be seen, Fig. 136. On the outside an epidermis which consists of a single layer of cells. Im- mediately inside this, a broad band of thick-walled paren- chyma forms the cortex. The cortex is a mechanical tissue and is the principal support of the plant. The remain- ing part of the stem is made up of scattered vascular bundles and ground tissue. TJiere is r^ rprnhinm anrl
FIG. 136. — A portion of a transverse section of stem of Maize, (x 20.) E, epi- dermis ; C, cortex ; VB, vascular bundles.
no_£rr»wth jn thickness ran take place a
result of tria
division of the cambium ring.
Structure of a Dicotyledonous Root.— If a transverse section of a very young tap-root of the Wallflower is examined the structure appears very different to that of the stem. On the outside the piliferous layer is formed ; this is another name for the young epidermis of the root. Many of the cells of the piliferous layer are converted into root-hairs, hence the name. A root-hair is unicellular and is produced from a single cell of the epidermis. Inside the epidermis, and limited internally as in the stem by the endodermis, is the cortex. The centre of the root is occupied by a vascular cylinder which consists of two masses of xylem and two masses of phloem. The xylem masses alternate? with the phloem masses. In the stem the protoxylem
no BOTANY FOR BEGINNERS CHAP.
points towards the pith^ in the root it points toward the cortex. The vascular cylinder is surrounded by the pericycle. Outside.
Piliferous layer with root hairs , . \
Cortex (parenchyma cells) . . . . I
Endodermis (single layer of cells). . \ Transverse section of
Pericycle (single layer of cells) . . ; Dicotyledonous Root.
Phloem masses\(In wallflower two, j
Xylem masses /which alternate) . . / Inside.
Growth in Thickness of the Root.— The roots of dico- tyledonous plants in which the stem increases in thickness themselves also grow in thickness. The growth in thickness of roots depends, as in stems, upon the cambium. The cam- bium, see Fig. 128, passes on the outside of the xylem, and on the inside of the phloem. As growth goes on the structure of the root becomes more and more like the stem, until in an old stem it is very difficult to distinguish the two. Periderm is also formed in a root from the pericycle ; this cuts off the cortex, and the root may be smaller after the second year of growth than during the first year.
The Structure of a Monocotyledonous Root.— In the root of a monocotyledonous plant there is a large central cylinder which contains, as a general rule, a larger number of distinct bundles of wood and bast. In some roots there may be as many as twelve alternating masses of xylem and phloem. The structure is essentially the same, but because the cambium layer is absent, there is no growth in thickness.
Expf. 103. — Select a young root of the Wallflower, and cut a thin transverse section from it, and mount in water. Examine under a low power. Note —
(i) The piliferous layer with its root-hairs.
(ii) The cortex, which is several layers of cells in thickness.
(iii) The endodermis, which is a single layer of cells surrounding the pericycle.
(iv) The pericycle, just within the endodermis.
(v) The alternating masses of phloem and xylem.
There are only two vascular bundles present.
EX.PT. 104. — Obtain a bulb of the Hyacinth, and from one of the adventitious roots cut a thin transverse section, mount in water. Examine under a low power. Note —
(i) The central cylinder, which is limited by the endodermis and the pericycle.
(ii) The very numerous masses of xylem and phloem, which also show the alternating arrangement already seen in the Wallflower.
ix THE HISTOLOGY OF THE SHOOT AND ROOT tti
The Structure of the Leaf.— Each leaf consists of the three tissue systems, but by far the largest portion is ground- tissue. The whole of the leaf is covered by the epidermis, and between the upper and lower epidermis comes the Mesophyll. Fig. 138. The mesophyll is built up of palisade cells above, and spongy parenchyma below. Between the spongy paren- chyma and the palisade tissue the vascular bundles run; these bring sap from the root to the cells of the leaf, and carry away the elaborated sap. The palisade tissue consists of regular, fairly elongated cells, which contain a very large number of chloroplasts, and only a few intercellular spaces. The spongy
H ,US ,UE
LS/
FIG. 137. — Transverse section of young root of Wallflower. {After Scott.) P, phloem ; X, xylem ; C, cortex ; P1, piliferous layer ; R, root hair.
FIG.
38. — Transverse section of leaf of Rhododendron. (X 250.) US, upper side of leaf ; LS, lower side of leaf ; P, palisade parenchyma ; S, spongy parenchyma ; VB, vascular bundle ; E, epidermis ; H, hypoderm.
parenchyma forms a loose tissue full of intercellular spaces. The cells of this tissue are not so well supplied with chloroplasts. The intercellular spaces of the leaf communicate with the stomata, so that any gas which may enter the stomata finds its way into the deeper parts of the leaf. The outside of the epi- dermis of the leaf is always of the nature of cuticle.
EXPT. 105. — Place a piece of the leaf of the Wallflower between little slabs of carrot, and with a sharp razor cut slices right across. Separate the transverse sections of the leaf so obtained in water in a
112
BOTANY FOR BEGINNERS
CHAP.
watch glass. With a camel's hair brush mount the thinnest one in water, and examine first with a low power then with the high power. Note—
(i) The upper epidermis, a single layer of cells with an outer cuticle.
(ii) The palisade parenchyma, which consists of cells, cylindrical in form, with a few air spaces between them ; the chloroplasts are very numerous in the cells.
(iii) The spongy parenchyma, which consists of loosely-arranged irregular cells with large air spaces between.
(iv) The lower epidermis with the stomata. Each stoma opens into a large intercellular space — the air chamber.
(v) That each stoma is a small opening between two guard-cells. Each guard cell is sausage-shaped and curved, the ends of the guard- cells being firmly joined together.
(vi) The vascular bundles have the xylem above and \h& phloem below. The xylem ends in the palisade cells and the phloem in the spongy parenchyma.
(vii) That the guard-cells contain chloroplasts, and that the other epidermal cells have no chloroplasts.
The Growing Point of the Shoot.— The growing point of the shoot consists of several layers of cells, which are meris- tematic in character. These cells are rich in protoplasm, and possess large nuclei, and are in a constant state of activity, i.e., growing and dividing to form new cells. From this meri- stem all the new tissues of the shoot are developed. There are three distinct layers of cells at the apex, viz. : —
(i.) Dermatogen.— On the outer FIG. 139.— Diagram of the grow- portion of the growing point a single mftoglnn;0f FR^W^em"; layer of cells is present. These divide PL, plerome. ' Up by walls being formed at right
angles to their surface. This layer
gives rise to the epidermis of the young shoot, and is called the dermatogen.
(2.) Periblem. — Below the dermatogen a layer of cells is found, which, at the apex, may be only one layer of cells thick, but lower down may be several cells thick. This is the periblem or young cortex, for it forms the cortex.
(3.) Plerome. — Underneath the periblem is found a group of cells, which gives rise to the whole of the vascular cylinder of
ix THE HISTOLOGY OF THE SHOOT AND ROOT 113
the stem, including the pith, the bundles, and pericycle. This layer receives the name oi plerome.
Formation of Leaves. — Leaves are formed from the der- matogen and periblem. The dermatogen grows out and the periblem follows. From the dermatogen the epidermis only is formed, the mesophyll and vascular bundles