An introduction to nature-study

Preface

One of the most encouraging of recent educational movements is the increasing importance attached, both in this country and abroad, to what is called Nature-Study. It is evident that the instruction contemplated differs as widely, on the one hand, from the traditional object-lessons on polar bears and ironclads, as it differs from formal Biology on the other. This difference is abundantly shown, not only by the circulars and syllabuses issued by our own Board of Education, but by the publications of the leading educational authorities of Europe and America. The aim of Nature-Study, as thus laid down, is not primarily the acquisition of the facts of natural history : it is rather a training in methods of open-eyed, close, and accurate observation, especially of familiar animals and * plants, which shall teach the student to see what he looks at, and to think about what he sees.

It is in a spirit of entire agreement with these views that this book has been written. No previous knowledge of Biology on the part of the reader is assumed, and technical terms have as far as possible been dispensed with. In drawing up the course, I have had in mind throughout the attitude of an intelligent youth of sixteen, and the work will be found to be well within the powers of such a student. Teachers will, however,

VI

PREFACE find no difficulty in adapting the exercises to the needs of younger pupils.

Care has been taken to select, as types for study, animals and plants which are at the same time representative and easily obtainable,1 and I have been further guided in the selection by the Board of Education Syllabuses of the King’s Scholarship Examination and Section I. of the Elementary Stage of General Biology, the subjects of which are included in the volume. The book has, however, a considerably wider scope than is indicated in these syllabuses, and will therefore, I hope, be found useful not only in schools and training-colleges, and to examination candidates, but also to members of field-clubs and to students of natural history generally. It has been neces sary to arrange the chapters with some attempt at logical sequence, but it is not supposed that this order will be adhered to in practice ; by the aid of the monthly naturecalendar, together with numerous cross-references, it will be found easy to take up the work at any point.

The chapters are divided into sections, each of which consists of two parts : First, precise instructions for practical observations and experiments, designed to exercise the reasoning faculties of the students ; and, second, a descriptive portion, in which the meaning and relation of the results obtained are discussed. At the end of each chapter is a number of additional exercises, either original or taken from past examination papers. Of the latter class, questions to which dates are affixed have been set by the Board of Education, while those marked “ N.F.U.” are selected from National Froebel Union tests.

1 If any difficulty is found in procuring plant-specimens, they may be obtained by post from the British Botanical Association, Ltd., Holgate, York. The names of dealers prepared to supply various animal-specimens are mentioned in the text.

PREFACE

Vll

In many cases, the exercises provide subjects for further observation and experiment, as well as for written description.

Much trouble has been taken in the selection of the illustrations, many of which have been expressly drawn or photographed for this book. Through the kindness of the publishers I have been able to include illustrations from Strasburger’s Text-Book of Botany , Parker and Haswell’s Text Book of Zoology , The Cambridge Natural History, and other books ; and Mr. Ernest Evans has courteously consented to the use of a number of figures from his Botany for Beginners. The following illustrations have been prepared from photographs supplied by Mr. J. C. Shenstone, F. L.S., Vice-President of the Essex Field Club : Figs. 27, 57) 6°) 65, 67 to 71, 74, 75, 80, 81, 83, 84, 85, 87, 89, 91, 92, 94, 95, 102 to no, 120, 134, 136, 145, 149, 152 and 153; while Figs. 180, 196, 200, 201, 203, 205, and 21 1 are reproduced, by permission, from Pike’s Woodland, Field, and Shore (Religious Tract Society).

Finally, I must acknowledge gratefully the continuous help which, at every stage in the preparation of the book, I have received from Professor R. A. Gregory and Mr. A. T. Simmons, B.Sc. — help as valuable as it was generous.

E. STENHOUSE.

Part I. Plant Life. Chapter

I. Seeds and their Early Stages of Growth, II. How a Green Plant Feeds, -

III. The Forms and Duties of Leaves,

IV. Buds. The History of a Twig, - V. How Stems do their Work, -

VI. Some Common Flowers,

VII. Grasses, -

VIII. Common Forest Trees, - -

IX. Fruits: How Seeds are Scattered, -

X. Ferns and Horsetails, - -

XI. Mosses, Mushrooms, and Moulds,

*

Part II. Animal Life

XII. The Rabbit: A Typical Mammal,

XIII. How a Rabbit Lives, -

XIV. Some other Mammals,

XV. The Pigeon : A Typical Bird,

PAGE

I

21 1 222 246 265

X

CONTENTS

CHAPTER PAGE

XVI. The Development and Education of the

Chick, - 282

XVII. Some Familiar British Birds, - - -301

XVIII. Frogs and Tadpoles, - - - . - - 332

XIX. The Habits and Life-Histories of Common

Insects, 349

XX. Some Crustaceans, Molluscs, and Worms, 372

XXI. Field-Work. Monthly Nature Calendar, 388

PART I.

Chapter I. Seeds And Their Early Stages Of Growth

1. THE STRUCTURE OF SEEDS WITH TWO

COTYLEDONS.

1. Preparation of the seeds. — Obtain several seeds of the broad bean, pea, mustard, yellow lupine, vegetable marrow, and sycamore ; soak them in cold or slightly warm water until they are soft enough to be cut through easily with a sharp knife. The time necessary will vaiy with different seeds according to the size of the seeds, and with the temperature of the water. The beans should be left in the water for a few days. When the seeds are soft enough, examine one or two of each, and in the meantime put about six of each (except the* mustard) in damp sawdust in a warm place. Put the mustard seeds on damp flannel in a saucer.

2. The outside of a broad bean. — Notice the flattened oval shape, with an indentation at one place (Fig. i). What is the colour of the skin ( seed-coat ) of the bean seed? Is all the skin of this colour ? A black scar extends along the edge from the indentation for about f in. What is this scar? If beans in the pod can be obtained, see that the scar is the place of attachment of the seed stalk. Make drawings to scale, showing side and edge-views of the seed. Wipe the bean dry and then

N.S. A squeeze it gently. Notice that a drop of water comes out at a point at one end of the stalk scar. There is evidently a little hole here. This little hole is called the micropyle. Mark its position by a dot on the drawing.

3. The inside of a broad bean. — With a sharp knife cut the seed-coat open, beginning at the side of the seed furthest from the micropyle, and carefully remove the seed-coat. Notice that near the micropyle the seed-coat forms a funnel shaped depression, and that the point of the funnel is at the micropyle. Does anything fit into the funnel ? A little cone may be seen to fill the funnel ; this conical body is called the radicle. Make a drawing of the seed after the removal of the seed-coat. Look at the edge opposite the radicle and notice that a crack divides the body of the seed into halves. Put the point of your knife blade into the crack, and gently force the halves apart. They come apart without tearing, showing that they are naturally separate, although they fit so closely together.

These two swollen bodies are called the cotyledons. Open them out and see, at the point where they join the radicle, that a little curved rod, evidently a continuation of the radicle, lies between them. This rod is the plumule. Take off one cotyledon, and make a drawing of the inner face of the other cotyledon, with the adhering plumule and radicle (Fig. 2).

4. Starch present in the cotyledons of the bean. — Scrape the inner surface of a cotyledon and then pour on it a drop of iodine solution.1 Is there any change? Pour also a drop of iodine solution on a piece of laundry-starch. Is a similar blue colour formed? What substance is probably present in the cotyledons of the bean?

5. The pea. —Examine a pea in a similar manner. Make drawings showing the stalk-scar , the micropyle , and the plumule and radicle with their manner of connection with the cotyledons. Does the end of the radicle point towards the micropyle ? How many cotyledons has the pea ? What shape and colour are they ? Do they contain starch ?

1 Made by dissolving one or two crystals of potassium iodide in about half a pint of water, and then adding iodine in small quantities until the solution is the colour of sherry.

THE STUDY OF SEEDS

6. The seed of the yellow lupine. — Compare this with the bean and the pea, and find out how many cotyledons it has, and whether they contain starch. Can you find the plumule ? It is very small, but occupies a position similar to that of the plumule of the bean. Does the end of the radicle point to the micropyle ?

7. The vegetable marrow seed. — Notice the peculiar shape (somewhat like a pocket-flask) of the seed, and the thickened margin which runs round it. Carefully cut the seed-coat away so as not to injure the part inside. How many cotyledons are present ? What is their colour ? Do they contain starch ? Can you see the plumule and radicle clearly ? If not, do not decide that they are absent, but leave the question to be settled later, when you watch a vegetable marrow seed “ come up.”

8. The mustard seed. — Notice how much smaller this seed is than the others. With a balance, find how many mustard seeds are equal in weight to one bean seed. Observe the stickiness of the seed-coat of the soaked seed, and then remove it carefully with needles, exposing two thin plates, each one folded on itself, and one tucked inside the other, like two sheets of note-paper. These are the cotyledons ; it seems that the smallness of the seed may be mainly due to the small size of the cotyledons. What is their colour ? Remember these characters and try, when you watch the young plants come up later, to find an explanation of them.

9. Tbe sycamore fruit. — The seed of the sycamore is enclosed in a case which has a wing attached to it. The wing, the case, and the enclosed seed together constitute the fruit of the sycamore. The fruits occur in pairs (Fig. 137). Notice that a cord runs out to each fruit from the stalk on which the pair of fruits is borne. Make a drawing of a pair of fruits, then separate the fruits.

10. The sycamore seed. — Cut open a fruit. Can you see anything between the seed and the fruit-case ? Would the hairy covering of the seed tend to keep it warm during the winter? Why ? Why do you prefer to wear flannel in winter and linen in summer? Flannel is more fluffy than linen.

Remove the seecl-coat carefully. Running down one side you will see a little curved rod. This is the radicle. Gently raise it with the point of your knife. Notice that the rest of the seed seems to consist of a green part, which is curled up. Uncoil the curls carefully. You find that they are two green leaves, fixed at the top of the radicle. These are the cotyledons. In the seed each cotyledon is first folded in two across the middle and then coiled up. Make a sketch showing the coils (Fig. 4). Can you see the plumule? It is just at the top of the radicle, where the cotyledons are fixed on.

Plants are living things. — One of our foremost naturalists 1 tells us that when he goes out into the woods, or into one of those fairy forests which we call fields, he finds himself welcomed by a glad company of friends, everyone with something interesting to tell. Such a feeling would be quite impossible to one who did not vividly recognise the fact that plants are alive ; for it is precisely this recognition or its absence which makes the observation of the forms and habits of plants fascinating or the reverse. Let the Nature-Student, then, at the outset of his work, keep the idea of life inseparably bound up with his every thought about plants It may at first require a little effort, but before long it will enable him to understand how the friendship of the more silent half of animate nature may form one of the great pleasures of life.

The study of seeds. — The manifestation of life is so striking, and the changes in form and size take place so rapidly, in the germination of seeds, that the study of plants cannot better be commenced than with this stage of their growth. The method has also the logical virtue of beginning at the beginning, or nearly so.

These early changes can be well observed by taking various common seeds, soaking them in water until they are soft, and then allowing them to germinate in damp sawdust,

1 Lord Avebury, The Pleasures of Life (Macmillan).

THE STUDY OF SEEDS taking a few out at intervals and noting their progress. The growth of the seeds takes plaee more rapidly if they are kept in a warm room, but in any case some days will probably elapse before much change is noticeable in them.

During the interval of waiting, some of the seeds themselves should be carefully examined, and drawings of all the parts should be made. The drawing ought on no account to be omitted. It compels the student’s attention to details which would otherwise pass unnoticed ; and a careful sketch

Fig. i. — A Broad-Bean seed. A, side view; B, edge view: st. sc., stalk-scar; m, inicropyle. (X§.)

is a much better record of an observation than any amount of description alone could be. The drawing need not be elaborate ; an outline pencil-sketch to scale will usually be sufficient.

The seed of the broad bean. — The seed of the broad bean (Fig. i) is large, having a diameter of perhaps an inch and a half, and a thickness of half an inch. In shape it is oval, but at one region the edge is indented, and a black scar (st. sc.) runs from the indentation along the edge for a distance of about three-quarters of an inch. This scar is the place of attachment of the stalk which formerly carried the seed in the bean-fruit (pod). It may be called the stalk-scar. If a soaked bean is wiped dry and then gently squeezed, a small drop of water escapes from the end of the stalk-scar nearest the indentation. The hole out of which the water comes is very small and difficult to see, but its position is thus made clear. This hole (m) is called the micropyle, — a word meaning the “ little gate.”

The bean seed is covered by a tough brown skin, the seed-coat (Fig. 2, s.c.), a funnel-shaped depression in which leads to the micropyle (///). The depression is occupied by a part of the seed which is shaped like a conical peg and called the radicle (/?) ; the point of the radicle is directed toward the micropyle. 'The great body of the seed is composed of

Fk;. 2. — Broad-Bean seed, seen irom the inside, after the removal of half the seed-coat and one cotyledon. Cot., the inner face of remaining cotyledon ; C' , area of attachment of other cotyledon ; m, micropyle ; pi, plumule ; R, radicle ; S.c., seed-coat ; st. sc., stalk-scar. (Xi.)

two fleshy, cream-coloured lobes, easily wedged apart by inserting a knife-blade between them ; these fleshy lobes are the cotyledons {Cot.). Between them, and continuous with the radicle, is a small yellow body, the plumule {pi.). The relations of the radicle, plumule and cotyledons are best seen by removing one cotyledon (Fig. 2).

A scraped cotyledon at once turns blue when a drop of dilute iodine solution is poured on it, thus showing the presence of starch. We shall see in Chapter II what use the growing seedling makes of the starchy food which is stored in its cotyledons.

THE STUDY OF SEEDS

The seed of the pea. — Except in size and shape the seed of the pea is very similar to the bean seed. Its form is spherical, and the scar left by the stalk which formerly attached it to the wall of the pea-pod (Fig. 3) is plainly to be seen.

Pointing towards the micropyle is the peg-like radicle ; the plumule lies between the hemispherical cotyledons. As before, the cotyledons can be proved to contain starch, by the blue colour which is formed when a drop of iodine solution is poured on the scraped surface.

The seed of the yellow lupine. —

The seed of the yellow lupine is

about as large as a pea, but it is

slightly flattened in shape. The

Seed-COat is prettily mottled ; Fig. 3. -Pods and Seeds of

F J 5 Pea. (x*.)

when it is removed, the greater

part of the seed is found to consist of two cotyledons. They are somewhat swollen, but they do not contain much starch. The plumule and radicle occupy positions similar to those of the bean and pea.

The vegetable marrow seed. — This seed has a rather curious shape, and somewhat resembles a pocket-flask. It is flattened, and the border of the seed-coat is thickened and of silky appearance, the rest of the “ skin ” having some resemblance to kid. The two cotyledons, which compose the greater part of the seed, are white and only slightly fleshy. The plumule and radicle are at the pointed end of the seed, and are difficult to see.

The mustard seed — In comparing the mustard seed with those already described, one is struck with the great difference in size. An average broad-bean seed weighs about 600 times as much as the mustard seed. While the two fleshy cotyledons make up the bulk of the seed of the bean, pea, lupine and vegetable marrow, the cotyledons of the mustard seed are thin and leaf-like. They are folded on themselves, one inside the other (as at g, Fig. 61), and enclose the radicle. The characters of the cotyledons

Fig. 4. — Sycamore Fruit, cut through in the plane of the wing. s.c., seed-coat (indicated by a thick, broken line); /.w., fruit-wall; h , layer of fine hairs ; R, radicle ; pi ., plumule ; cot. /, cot. 2 , cotyledons (diagrammatically shaded). (X2.)

account very largely for the small size of the mustard seed. It will be seen, when the growth of the young plants is watched, that the difference is associated with the special duties which the cotyledons perform in the various cases.

The sycamore seed — What is generally called the seed of the sycamore is really a fruit. The fruits are in pairs (Fig. 137), and each half consists of a flat wing and a rounded case in which the seed itself is enclosed. The round seedcases of the two fruits are connected together. When they come apart, a scar marks the place where they were formerly in contact, and a little cord runs out to each fruit from the stalk on which the pair of fruits is borne.

Between the sycamore seed and the wall of its case is a layer of fine hair (h, Fig. 4), which forms a warm nest for the seed in winter. The seed is surrounded by a thin, brown seed-coat, and consists mainly of two cotyledons, but these are very different from any yet described. Each is a green leaf, measuring, when unfolded, about an inch in length. It is first folded across the middle of its length, and then rolled up into a close coil with its fellow. The coils are very plainly to be seen when the seed coat is removed, or when the whole seed is cut through, by a sharp knife, in the plane of the wing. Running down one side of the seed is a green rod, the radicle (R, Fig. 4). The two cotyledons (cot. 1 and cot. 2) spring from its upper end, and between them is the tiny plumule (//.)

The sycamore seed bears more resemblance to the mustard seed than to the others, but it is on a much larger scale. In each of these two seeds the cotyledons are plainly leaves, while in the others their nature is disguised by the great accumulation of stored food in them.

2. THE EARLY STAGES OF GROWTH OF SEEDS WITH TWO COTYLEDONS.

If the seeds which were sown in damp sawdust and on flannel are kept warm they will soon be ready for study. You should remember that at present your object is not so much to rear the plants as to find out how they grow. As soon, therefore, as any sign of growth is to be seen when you take a seed out, you should begin to examine them at regular intervals, taking one or two out every day and leaving the rest to continue their development. Keep the sawdust damp, but not wet.

1. The pea and bean. — (a) Ge7ieral developmettt. — Very soon the seed-coat splits at the micropyle-end of the stalk-scar, and

IO the end of the radicle protrudes. Does the radicle grow upwards or downwards ? Observe that even if the seed was so planted that the micropyle was at the top, the radicle turns over and grows straight down. Turn over a seedling and see if you can persuade the radicle to grow upwards. Open a seed when the radicle is about an inch long, and see what the plumule is doing. It is still enclosed in the seed-coat, and lies between the cotyledons, but is larger than at first. As the growth proceeds the cotyledons begin to separate near the top of the radicle, and you can get a glimpse of the plumule.

(b) The growth of the radicle. — Day by day the radicle becomes longer. Is it all growing longer, or does the increase in length take place more at one part than another? To answer this question, take five or six inches of cotton thread and moisten the middle part with Indian ink. Lay the seed on a flat ruler, so that the radicle lies over an inch divided into — say — tenths. Hold the thread tight, and press the inked part gently on the radicle, making about five marks at equal intervals from the point upwards. The ink will dry almost immediately. Then carefully replant the seed, taking care not to injure the radicle. After a few days take it out again, lay it once more on the ruler, and measure the distance between the marks.

The radicle is evide?ttly the young root.

(c) The root- cap. — Hold up the radicle to the light, and examine its tip with a lens. Try to see that the tip is covered by a little cap, somewhat like a very small thimble. This is called the root-cap.

id) The root-hairs. Hold a seed, with the radicle about an inch long, against a dark surface. Is the surface of the radicle smooth, or can you see any fluffiness on it? Is all the radicle fluffy, or only a part ? Which part ? As you examine older and older seedlings notice how much of the radicle is fluffy, and where the fluffy part is. The fluffy appearance is caused by fine, closely-set hairs, called root-hairs.

(e) The plumule. — Wow soon after planting does the plumule become free ? Does it grow upwards or dowm wards ? The plumule is evide?itly the young stem.

As soon as the young stem is old enough mark it with Indian

1 1 ink as you marked the young root, and replant it to find if there is any difference in the rates of growth of its different parts.

(/) The fate of the cotyledons. — From time to time examine the cotyledons and notice that as the seedling grows larger they become more and more shrunken. Something is evidently being taken from them, perhaps to feed the young plant. We shall inquire into this by further experiment (Chapter II.).

Do the cotyledons remain in their original position, or are they carried upwards with the growing stem or downwards with the growing root ?

2. The yellow lupine.— In the same way observe how this seed grows. Do the cotyledons shift their position or change in colour? Do they become leaflike? How do they differ from later-formed leaves ? What becomes of them at last ? What becomes of the seed-coat ?

3. The mustard seed. — Notice that, soon after the radicle has come out of the seed- coat, a sort of hump forms at its upper end, and at length the cotyledons are pulled out of the seed-coat and turn up towards the light. What is their colour? Observe that the two cotyledons are soon raised on the end of a little stalk. Like the cotyledons of the yellow lupine they are plainly leaves. Notice their shape. Are they of equal size? Why not? When they are about three inches above the seed-coat gently separate them and notice the little bud between them. Draw the seedling. How large can you get a mustard seedling to grow on damp flannel ? Plant a few mustard seeds on earth, and notice the difference between the shape of the cotyledons or seed-leaves and that of the leaves which appear later. What becomes of the cotyledons ?

4. The vegetable marrow seed.- Make similar observations upon the vegetable marrow seeds, noticing particularly whether the cotyledons remain in their original positions and shrink up as the plant increases in size, or whether they are pulled out of the seed-coat by the elongating stem, and become green and leafy. How does the plant hold down its seed-coat whilst it pulls out its cotyledons ?

5. The sycamore seed. — From what you have seen of the cotyledons of the sycamore seed, will you expect them to behave like those of the mustard seed, or like those of the pea and bean ? Even in the seed they are green, and plainly leaves. How do they escape from the seed-coat? What is their shape? Do they come out before or after the radicle ? Do they get any larger as the stem grows ? How large can you get a sycamore seedling to grow in damp sawdust ? As large as a seedling of pea or bean ? Plant some sycamore seeds on earth and compare the shape of the cotyledons with that of the next-formed leaves. How soon do the “true” leaves appear after the cotyledons have escaped from the seed ? Do any “ true ” leaves grow on the plants in sawdust ? What becomes of the cotyledons at last ?

The embryo. — The plumule, radicle, and cotyledons, which have now been seen in the seed, form the embryo of the plant. The adult plant will be wholly formed by the growth and development of these parts, and we must now follow carefully the changes which take place when the seed germinates, and try to find out what becomes of each part. It is better to put the seeds at first in damp sawdust rather than in earth, as the young roots can then be more readily cleaned and observed. With small seeds the early stages of growth are better seen if damp flannel is used.

Germination. — Under the influence of moisture and warmth the embryo in the seed begins to swell and unfold its parts. The radicle makes its appearance first (Fig. 5), breaking through the seed coat at the micropyle; it is the young root. The radicle always grows downwards, that is, toward the centre of the earth. If the seed lies in such a position that the micropyle is directed upwards, the point of the radicle turns over and grows downwards as soon as it escapes from the seed-coat. As the young root becomes longer and thicker (Fig. 6) the seed-coat opens more and more, showing the cotyledons beneath, and these, too, are gradually forced apart.

The cotyledons. — During the germination of various seeds, a very marked difference in the behaviour of the cotyledons is to be seen. In the case of the bean and pea the cotyledons remain in their original positions, partially enclosed by the split seed-coat. Presently a hump (Figs. 6 and it) form at the upper end of the radicle, as if the plant were making an effort to pull its plumule out of the seed. It soon succeeds (Fig. 12), and the plumule turns up to the light. It is the young stem. At its end is a little bud, formed by a number of small, overlapping, green leaves which surround the growing point. Henceforth the stem grows upwards, that is in a direction precisely opposite to that of the root’s growth. Both stem and root are attached to the cotyledons, which gradually shrivel up as the stem and root become larger and larger.