The Study of Plant Life

by Marie Carmichael Stopes

SUMMARY OF PART I.

We have now done a number of experiments with plants, and found out many facts about their way of life, and I think you will agree that we have collected enough evidence to prove the statement made at the beginning of Chapter II.—that on the whole plants show the same “signs of life” as do animals.

We have seen that like animals they breathe in a part of the air, and that they breathe out with the air the added carbonic acid gas, which is the characteristic “waste product” of the out-breathing of animals.

They practically “eat” when they take in substances as food into their bodies, even though they have no gaping mouths which can open and close. We noticed, too, the interesting parallel between young plants and young animals, where both (the plants in the food in the seed, the animals in their mothers’ milk) are supplied with ready-made food at first, and as they get older have to find what food they require for themselves. As regards their feeding, the plants do more work than the animals, for they manufacture the starchy food for themselves out of simpler elements, while the animals require their starch to be ready made.

Then the fact that plants grow, increasing in size and forming new structures, has been known to you ever since you were a baby yourself. Although we noticed here an important difference between the kind of growth in plants and animals, yet the growth itself is alike in the two cases, for both plants and animals build up their living bodies out of simpler substances which they take in as food and change till the not-living food becomes part of themselves and is living.

Movement is not nearly so great in plants as it is in animals, and most plants are firmly fastened in the ground. Yet there are some plants in which we can see very rapid movements of some of the parts, while many simple little plants living in water can swim actively about like animals. All plants show some form of movement, though it is generally slow.

As a result, we find that all the signs of life we noted in animals, viz. breathing, eating, growing, and moving, are to be found in plants, and we must look on them as being just as much alive as animals. We can see that their mode of life and the work they do are distinctly different from those of the animals, but they are no less vital, and important for the world as a whole.

PLATE II.

A WHOLE PLANT, TO SHOW ALL THE PARTS

A POPPY

PART II.
THE PARTS OF A PLANT’S BODY AND THEIR USES

CHAPTER XI.
ROOTS

If you have a garden of your own, or have even watched another person gardening, you must have found out that it is not always an easy thing to get rid of the weeds, and that when one tries to “pull them up by the roots,” they often resist it very strongly indeed. If you have never done this, try to pull up a large grass tuft or a hedge mustard, or any fairly big common plant, and you will find that often when it does not look very strong it may be extremely difficult to get it completely out of the soil, and even when it comes out you may find that you have not got it quite whole, for the finer branches of the root will generally break off. Now this shows us one of the uses of its roots to a plant; they keep it firmly in the soil, and prevent the wind from blowing it away, and people or animals from overturning it too easily.

To see the form of a complete root it is wise to choose a fairly small plant, let us say a daisy, wallflower, candy-tuft, or young holly; then loosen the earth all round it and pull it very gently from the soil. Shake off the mud and then wash it clean and spread it out on a sheet of white paper so that you can examine it properly. Notice that there is a central chief root, with many side branches which have again finer and finer branchlets (see fig. 36). At the tip of the very finest you should see a number of delicate hairs, the root hairs, but it is very possible that you will have torn these off with the soil. To see them best, look at some of your seedlings which have grown in moist air, where they are very well developed (see fig. 8). In any of these plants you will notice that the main root seems to be a downward continuation of the main stem, and that the side roots come off all round it, just as was the case in your bean seedlings (see figs. 36 and 7). Such a root is called a tap root.

Fig. 36. Root of a young Holly: l, level of soil; s, stem; c, chief root with many side branches and finely divided rootlets.

Now dig up a small grass plant and compare its root with these, and you will see that there is no main root, but very many roots coming off in a tuft from the base of the stem, just as was the case in your corn seedlings (see fig. 37). The difference between these roots and tap roots is not of much importance as regards the actual work they do but is one of difference in form; the finer branches in both are very similar and have the same work to do.

Fig. 37. Grass plant, showing the many finely divided roots.

If you leave the plants you have pulled up lying in the air for an hour or two, you will find that they will wither, the leaves becoming quite limp and the whole plant drooping. Now place them with their roots only in water, and you will soon find that they are beginning to revive. They will revive fully and live a long time if their roots are kept in water. This reminds us of the second very important use of its roots to a plant, which we have already found out (see Chapter IV.), and shows us again that the roots absorb water and keep the whole plant supplied with it. Of course you know that cut flowers can drink up water with their stems, but that is only for a short time, and is not quite natural. The special part of the rootlet, which does the actual absorption, is the part near the tip which is covered with root hairs. You have already seen these root hairs in the course of your work (see pp. [13] and [15]).

There are then two chief duties of roots, to absorb water from the soil for the whole plant, and to hold it firmly in the ground. The fine fibres of the root, which are so much divided and run in the soil, serve both these purposes, as they expose a large area to contact with the soil, and so can absorb much from it, as well as getting a good hold of it.

As well as these two chief functions, there are many other pieces of work which roots may do, and according to the special work they take up, so they become modified and look different from usual roots.

Fig. 38. Tap root of Carrot, swollen with stored food.

One thing they often do is to act as storehouses of food. For example, examine the root of a carrot. The part we commonly call the carrot and which we eat, you will see is really the main axis of the tap root, and has the little side roots attached in the usual way. The unusual thickness of the main root is due to the large quantities of food which it stores. Just in the same way radishes and many other plants have their main roots very thick and packed with food, while dahlias have their side roots thickened in a similar way (see fig. 39). Such modified roots, which look quite different from ordinary ones, are called Storage roots, and if you examine many of them you will find them packed with starch (see p. [11] for iodine test).

Fig. 39. Dahlia, with storage roots packed with food.

Although it is general for the roots to hold the plant firmly in the ground, in some cases they grow out of the stem in the air and help to hold it up against a tree or wall, or some support, as in the case of ivy. If you pull off a branch of ivy which is climbing up a tree you will find that all along the back of the stem there are tufts of short thick rootlets which often come away holding a piece of the bark of the supporting tree. These roots, you will see, do not come out in the usual way from the main root or base of the stem, but come out all along the stem itself (see fig. 40). Such special roots are called “Adventitious,” and they grow from the stem wherever they are needed.

Fig. 40. Adventitious roots growing out from the stem of Ivy between the leaf stalks.

Adventitious roots may also come out from a wounded plant which has had its true roots cut away. For example, take a piece of Forget-me-not stem without any roots, and slit it at the base, and put it in a glass of fresh water. After a week or so you should see little white roots growing out from the stem into the water, and if you let them get strong you may then plant the sprig and get a new forget-me-not plant from it. In this and all “cuttings” adventitious roots growing out from the stem do the usual work of roots. There are many other kinds of adventitious roots, but we must only mention the orchids, some of which have long tufts of roots which grow out irregularly from the stem and hang in the air. These are special air-roots, and grow on many orchids, but also on some other plants which live attached to trees and absorb the water out of the air instead of from the soil (see fig. 41).

Fig. 41. Tufts of air roots of an Orchid.

Fig. 42. Supporting or stilt roots growing out from the base of a small Palm in a pot.

There are many other curious roots, particularly in plants which grow in tropical countries, e.g., the stilt roots which come out from the base of the stems of many palms and make tripod-like supports (see fig. 42), and others which grow from the high branches to the ground like pillars, and prop up the heavy trunks. However, we do not need to go so far to find very many different kinds of roots, and if you examine carefully those of the plants growing in our woods and lanes, you will find what a number of extra pieces of work they can do, in addition to their two chief duties of drawing in water from the soil, and holding the plant in its position in the earth.

CHAPTER XII.
STEMS

Examine the stem of a sunflower; it is tall and straight and grows upright in the air, bearing leaves which stand out from it.

In a young holly, and many other plants, we find growing out from the central stem smaller side branches which bear the leaves. As we have found already (Chapter VI.), the leaves are the active parts of the plant and do the food-building, so that the stem is chiefly useful as a support, which keeps them in a good position as regards the light and air. In general, we do not see much of the stem because it is largely hidden by the covering of leaves, so that if you want to study stems you should go to the woods in the winter when there are no leaves on the trees, and you can see the form of the branches themselves.

In big trees, such as the oak and beech, the stems are very important, and the chief stem or trunk becomes very thick as it gets old. It is made of hard wood which is tough and strong, for such high trees have to bear great strain from the winds, as well as the weight of all the leaves. If you go into the woods when it is very windy, and watch the thick wooden boughs swaying, boughs which you could not move, you will see how much force the wind may sometimes have. The branches need all their strength in the summer to support the curtain of leaves which catches the wind. In a big tree we find the few chief branches thick and strong, but there are many hundred smaller ones, some of them dividing to quite delicate branchlets which bear the leaves, so that the whole tree body is very much complicated (see fig. 43).

Fig. 43. Much-branched stem of the Oak.

Each kind of tree has a way of branching which is characteristic of its species, so that even without leaves or flowers a woodman can tell what a tree is. This one can learn by practice in the woods, but to begin with it is rather difficult. Without going into detail, however, we may notice great family differences, such as exist between a larch or a Christmas-tree and an oak. In the first two there is one straight main trunk, with side branches at very regular intervals (see fig. 44), and in the oak the main thick trunk soon bears several large branches nearly equalling the main stem; these divide again and again in a rather irregular fashion (see fig. 43).

Fig. 44. The Larch, showing its strong central trunk and more delicate side branches.

In many of the smaller plants the stems are not strong enough to stand up against the wind, and they simply lie along the ground or support themselves by growing among other plants, such, for example, as the common Stellaria, where the stem is very delicate indeed (see fig. 45). Then again, if you pull up a large water-lily, you will notice how soft and limp the long leaf-stalks are. They cannot support themselves at all in the air, though they were upright in the water. This is because the stalks get their support from the water which allows them to float up, so that the plant does not build a strong stem. You will find that plants are very economical in their use of strengthening material, and never waste it where it is not wanted. If you remember this, and then study all the stems you can, and note when and where they are strengthened, you will find what good and economical architects plants are.

Fig. 45. Delicate stem of the Stellaria, partly lying on the ground.

As well as supporting the leaves, the stems have another very important duty, something like that of the roots. Just as the roots absorb the water from the soil and carry it up, passing it on to the stems, so the stems carry it on to the place where it is finally used, that is, to the leaves. In both stems and roots there are channels or “water-pipes” which carry water about, as well as other special “pipes” which carry the manufactured food.

So that the two chief duties of stems are to act as supports for the leaves and flowers, and to carry the food materials and water between the roots and leaves.

Just as we found in the case of the roots, there are many extra duties which the stems may take over, and as a result, we find great variety in the appearance of stems. For example, in some plants the stem does not grow up into the air at all, but creeps along just below the surface of the ground. This you may see if you dig up a Solomon’s Seal or an iris, when you will find that the stem looks very like a thick root running horizontally in the ground. That it is really a stem you can tell from the fact that the leaves grow out from it, and you can see the scars of old ones as well as the present leaves, and also some little brown scaly leaves, and a large number of adventitious roots. The stem is rather swollen with food materials which are stored up in it, and it is not coloured green like many of those growing in the air. Such a stem, creeping under the earth, and only sending its green leaves into the air, has a special name, and is called a Rhizome. Many plants have such stems, particularly ferns, as you can see very well if you dig up a bracken.

Fig. 46. Underground stem of the Solomon’s Seal, called a Rhizome. It has many scaly leaves, s and a shoot A which will come out into the air bearing green leaves. B is the scar left by the similar shoot of last year. r are the adventitious roots which come out all over the stem.

Fig. 47. A Potato: s, the stem attaching it to the main stem; e, scale-leaf; b, bud in its axil; t, tip of the Potato with several buds, some of which are sprouting.

Some of the underground stems which store food are still more modified, so that it is very hard indeed to tell what they really are. This is the case in the potato, which you would naturally think at first is a swollen root, like those we saw in the dahlia (fig. 39). That it is really a stem you can see by examining the “eyes” carefully. The eyes (see fig. 47) are buds with scale leaves round them, and at the tip of the potato we can see several such buds together (fig. 47 t). The whole potato is a very much swollen stem which is packed with food and has all its other parts so reduced that it is difficult to recognise them. Such special stems are called Tubers.

Certain stems take on the work of leaves, and sometimes they are so much modified for this that the plant has no true leaves at all. This is what has happened in the case of a cactus. If you can get a cactus, examine it carefully and you will see that the whole plant consists of a thick mass of green tissue, which apparently is not divided into stem and leaves. But the truth is that the whole of the thick mass of tissue is the stem, and the little tufts of spines and hairs are really reduced leaves. So that in the cactus the green stem does all the food building work instead of the leaves.

Fig. 48. Cactus plant, showing its fleshy stem, which is green, and does the food building for the plant. The tufts of spines and hairs represent the leaves.

In some plants this is not so much marked, even though the stem does some of the work for the leaves. In such cases the stem is generally green and broad or winged and the leaves small, as in our common broom and the whortleberry, where the leaves very soon drop off. Quite a number of plants have stems which do this, and it is sometimes a great advantage to the plant, for the big leaves are often very wasteful of water, as you will see in Chapter XVIII.

In other cases we find that the side branches of stems may be modified to protect the plant, and so take on the form of strong spines or thorns, as in our blackthorn, where the sharp pointed spines are modified side shoots.

There are many other pieces of work which stems may do; we must just mention the climbing and twining stems, where the stem is delicate and requires to be supported, which we are going to examine more carefully in Chapter XIX.

Sometimes, instead of continuing to grow into the air, the stem may bend over into the earth again, as often happens in big bushes of bramble (see fig. 49), and then from the tip of the stem a number of adventitious roots (see p. [56]) grow out and hold it firmly in the ground. If, then, this branch gets separated from the rest of the plant, it can build a complete new individual.

Fig. 49. Leafy branch of Bramble which has bent into the earth and given rise to a cluster of adventitious roots at the tip; l, level of soil; P, point where the branch was cut from the parent plant.

In the case of the bramble notice how the leaves get smaller and smaller towards the tip of this branch as it bends down to the earth, and of course, they do not develop at all as true leaves under the soil (see fig. 49).

From these examples, and the many others you should be able to find for yourselves, you see that stems may take on other duties beyond their two chief ones, but that, however much they change their form and appearance, we can always find out that they are really stems by studying them with a little care.

CHAPTER XIII.
LEAVES

The late spring and summer are the best times to study leaves, for, as you must have noticed, the woods begin to lose their green in the autumn, and the leaves have fallen in the winter. This tells us that the fresh greenness of the leaves (which you know is so important for the plant) does not last very long, and when they are no longer green the leaves are useless and drop away. As you know, the chief work of leaves is to build starchy food, for which they require their green colour.

Fig. 50. Simple leaf of the Cherry.

When you go into the woods or gardens to study the leaves, first look at single ones, collecting as many kinds as you can. Though their shape varies very much, you will find that in almost all cases they are green, expanded, and flat. Let us first examine a single simple leaf, like that of a cherry. You will see that the expanded part (called the leaf blade or lamina) narrows down to a small stalk, which connects the blade with the stem from which the leaf is growing; this stalk is called the leaf stalk or petiole. Then at the base of it, just where it joins on to the stem, there are two little leaf-like structures which are not true leaves, but which belong to the leaf and are called stipules; they are attached to the base of the petiole, which spreads out to clasp the stem, and is called the leaf base (see fig. 50). Such a leaf shows us all the parts of a simple leaf; but some leaves have no stalks, others no stipules, and so on.

Fig. 51. Compound leaf of the Rose.

Let us compare a rose leaf with the simple leaf of a cherry, oak, or beech. In the rose you will find five or seven small leaflets arranged on a single main stalk, and each of these leaflets separately is very much like a single leaf of the beech. Such a leaf as this we call compound, for it is divided up into several parts, each of which looks like a whole leaf (see fig. 51).

Leaves are of very many different kinds and shapes, and special names have been given to each kind, which you can look up in a book if you want to classify them.

Fig. 52. Peltate leaves of Nasturtium, showing the stalk attached in the middle of the lamina.

Let us just notice a few of the types. The cherry, beech, and others which are simple with slightly pointed ends, we may call by the proper term ovate. Then there are leaves like those of the nasturtium, where the leaf blade is circular and the leaf stalk does not come in at the base of the leaf, but is attached to the middle of it; such leaves as that are called peltate.

The broad or rounded leaves, which spread out like the palm of a hand, such as the ivy (see fig. 26), are called cordate or lobed, and when compound, as are those of the horse chestnut, palmate.

Fig. 53. Needle leaves of Pine growing in pairs.

All the grasses and the many plants belonging to their family have very long, narrow leaves, which we call linear, while those of the pine trees are sharp and pointed, and are called needle leaves.

Fig. 54. Seedling of Rose; (c) cotyledons; (a) next leaf, simple, but toothed; (b) next older leaf divided into three leaflets.

As we noticed in comparing the leaves of the rose and cherry, some plants have very much more complicated leaves than others. Now such complicated structures do not develop on a plant all at once, as you can see if you examine a very young rose seedling. The first pair of leaves or cotyledons do not remain inside the seed as they do in the bean, but grow outside into the air and become green; they are quite simple leaves with smooth edges. The next leaf which unfolds is also simple, but it has a deeply toothed edge (see fig. 54), while the leaf following that is a compound leaf, divided into three leaflets. The other leaves gradually get five and then seven leaflets as the seedling grows up.

This is just one example of what usually happens in the history of plants with compound leaves, or leaves with any special shape; the young seedling’s earlier leaves are much more simple than the later ones. You should collect as many seedlings as possible and make drawings of them if you can, to show the various stages leaves pass through before reaching the full-grown complex form.

Fig. 55. Skeleton of a leaf, showing the fine network of the small veins.

Now let us look again at the actual structure of leaves. Hold up those of the rose, or lilac, or lime tree to the light, and look at the “veins” running in them. There is a chief central vein or mid-rib, and from it a number of side branches come off and divide and branch again and again till they form a fine net-work throughout the whole of the leaf blade (see fig. 55). If you now look at a grass or lily leaf, you will find that there are very many veins about equally important, running from end to end of the leaf and remaining nearly parallel to each other. This difference between parallel veins and net-work (or reticulate) veins is quite important, and is one of the characters which help to separate two very big families of flowering plants (see Chapter XXIII).

Fig. 56. Alternating pairs of leaves of the Dead Nettle.

Fig. 57. Pair of Honeysuckle leaves with no leaf stalks.

Now let us see in what way the leaves are arranged on the stem. If you pick a branch of dead nettle you will see that the leaves are attached by their stalks to the stem in pairs, two leaves coming off from the same level at opposite sides of the stem (fig. 56); while fig. 57 shows that the leaves of honey-suckle really do the same thing, only they grow out directly from the stem as they have no leaf stalk. Now look once more at the leaves of the dead nettle, choose one particular pair to start with, and then look how the pair above it are placed. You will see that they do not lie directly above the pair you chose, but are arranged on the opposite sides of the stem, so that the two pairs alternate. If then you look at the pair next above them, you will see that they are arranged in just the same way as the first pair, and so alternate with the second. In this way every pair of leaves on the stem alternates with the pair above and below it. Now examine a pear or cherry twig, and you will see that the leaves are arranged singly on the stem. Fasten a piece of thread to the stalk of one leaf and twist it round the base of the next, then on to the next above and so on. You will find that the thread makes a spiral round the stem, and finally comes to a leaf higher up it, which lies exactly above the one you started from. Very many plants have their leaves arranged like this in a spiral on the stem with the youngest at the top. There are different kinds of spirals for the arrangement of leaves in the different plants. You can see this by making the spiral of thread and counting how many leaves you pass on your way up the stem till you reach the leaf which lies just immediately above the one you start from.

Fig. 58. Branch of Cherry (leaves cut off to make it clearer), with a string twisted from leaf stalk to leaf stalk, showing the spiral arrangement. Note that leaf 5 is the first to come immediately above the one you started from.

Fig. 59. Leaves arranged in a whorl in the Horsetail.

Sometimes the leaves are arranged in a circle all round the stem at the same level; this is the case in the horsetail (see fig. 59), and such an arrangement is called a whorl, but it is not very common in plants.

In the goose grass the leaves look very much as though they were really in a whorl (see fig. 60), but there are only two true leaves; the others are the stipules, which are so much like the leaves that it is very difficult to tell them apart.

Fig. 60. Leaves of Goose grass looking like a whorl.

As we found out already, leaves require light and air, and usually arrange themselves so as to get them; hence, in a general way, we may observe that the leaves all grow to face the light. If you go under a beech tree, for example, and look up, you will find that you can see nearly all the big branches on the inside, while the leaves form a covering or dome on the outside. Special cases of leaves so arranged as to get a good light we noticed before (see pp. [36] and [37]).

As well as their own particular work, leaves may take on extra and different work, so becoming modified to suit their different occupations, and unlike true leaves. We already noticed in the cactus (see fig. 48) that the leaves become like sharp spines which protect the fleshy stem, and can do none of the usual work of leaves, because they have lost their green colour.

Fig. 61. Leaf of Pea, showing leaflets modified as tendrils (t); expanded leaflets (o).

In some plants leaves, or parts of leaves, may change into fine tendrils which become very sensitive to touch, and can twine round supports and cling to them, and so help the plant to climb. Such tendrils we saw (fig. 31) move very quickly; they are quite different in their structure from ordinary leaves. This happens in many plants, and you may see it very well in the sweet pea (see fig. 61), where only two leaflets of the compound leaf remain leaf-like, the others having been changed into tendrils.

When we come to look at Flowers, with all their special shapes and brightly coloured parts, we are really looking at modified leaves. But they are so very much modified that we have come to consider flowers as things by themselves, and so we will study them later on.

Some plants which do not have true flowers, yet have leaves of two kinds. For example, the “flowering fern” has the usual green leaves and others which form rather brownish golden spikes, and which are covered with spore[6] cases. Then again, some leaves are very specially modified and are changed from the usual structure in order to act as traps for insects (see Chap. XXI.).

Other leaves, instead of being very much developed, or specially developed along some line, are simply reduced, that is, are very little developed indeed. For example, as you saw in the under-ground part of the potato and many rhizomes growing horizontally, the leaves never become large and green, but remain as simple brown scales. Some scale leaves have quite a special work to do in the way of protecting the very young green leaves while they are in the buds, and we will look at these carefully in the next chapter.

We have now seen that leaves, like all the other parts of the plant, can modify themselves in a very great number of ways, and may do many extra pieces of work above and beyond their chief work of food manufacture.

CHAPTER XIV.
BUDS

The proper time to study buds in nature is the spring, but then you will have to wait long to see all the different stages of their slow unfolding. But they can be made to open artificially, and it is really wise to study buds in winter, when there are not so many other things to do. You can arrange this very well if in the late autumn you cut off fairly big branches with buds on them (horse chestnut is particularly good for this) and keep them in a warm room. You must, of course, keep the cut ends of their stalks in water, which you should change every three or four days, sometimes cutting off a piece from the ends of the branches so that they have a fresh surface exposed to the water. In this way they should live for months, and may just begin to unfold and show fresh young green leaves about Christmas time, when the buds on the trees out in the cold are still tightly packed up.

Fig. 62. Buds of the Horse Chestnut beginning to unfold.

Watch the buds as they unfold, and you will find that round each bud are several dry brown scales; these drop off, and within them are more green, leaf-like scales enclosing the true young leaves, which are still curled up and very small when they first come out.

If you examine a big bud which has not yet begun to unfold, and carefully pull off all the parts separately with the help of a needle and knife, you will see how the outer scales fold over one another like a coat of mail, and where they are exposed to the outside air they are hard and shiny, and in many plants are covered over by a sticky waterproof substance like tarpaulin. These outer scales keep off the rain and snow, and keep the inner parts dry and unharmed. Within them the scales are softer and often quite green, and they, too, wrap round each other, so that there is no crack left which could allow the cold rains to enter to the little leaves within. In many cases also the young leaves are wrapped up in soft, long hairs which look almost like cotton wool. These hairs grow on the leaves themselves, and you can see them after they have opened out, but as the leaves are then much bigger, the hairs are scattered further apart and do not show so much.

Fig. 63. Bud of the Horse Chestnut, showing the overlapping of the scales.

If you cut right through the length of a bud with a sharp knife, you will see how all these scales and young leaves are packed together, as in fig. 64.

Fig. 64. Bud cut through lengthways, showing the bud-scales and young leaves packed within them.

Take another bud and carefully pull off all the scales one by one and lay them in a row, beginning with those right outside; you will see that they get less scale-like and more like real leaves as you go in towards the centre of the bud (see fig. 65). The outside simple brown scales scarcely look like leaves at all, but the inner ones are green and soft, and in some plants, those right inside have quite a leaf-like appearance.

Fig. 65. A series of bud scales from a Horse Chestnut; (a) and (b) are entirely hard and brown; (c) and (d) are brown at the tips and green at the base, where the others cover them; (e) is quite green, soft, and leaf-like.

This helps us to see that bud scales are really only modified leaves, which are altered for their special work of protection of the young leaves through the winter.

Of course, you know that the buds are already on the trees in the late autumn after the leaves have fallen; but have you seen the buds already there in the summer while the leaves are still fresh and green? If you look for buds you will be sure to find them, and at the same time you will learn where they grow on the stem. You must look right at the base of the leaf stalk, in the angle made by the leaf stalk where it joins the main stem; this is called the axil of the leaf, and it is in the axil of the leaf that you will find the small green buds in summer-time. These buds grow out in the following year, so that a new leaf comes in very nearly the same place as the old one, or, what is more usual, there grows out a new branch which may bear several new leaves. Now examine a twig of horse chestnut or sycamore from which the leaves have dropped; notice that, where the buds are to be seen on the stem, they lie immediately above scars of a definite shape, which are the scars left by the fallen leaf stalks, as you can see by comparing them in the autumn with leaf stalks which are just falling away (see fig. 66, l, b, and s).

On the stem there are other scars, which are different from the ordinary leaf scars, and which are like bands of fine lines round the stem. What are these? Now if the single big leaf stalk leaves its scar so clearly on the stem, what kind of scar would a number of thin scales lying close together be likely to leave? Will it not be a number of narrow scars in a band, just such a scar as we have here (fig. 66, a, a¹, and a²). If you mark a bud on a tree or one of the branches in your room and watch it unfold, and keep a note of it till the autumn, you will find at its base where the bud scales were, that there is then a scar just like this. Whenever you see such a scar you will know that it has been left by a bud. Now you know that, as a rule, trees have buds only once a year, so that each of the bud scars along the stem must represent a past year’s bud, and if you count these scars along the length of the stem it will tell you the number of years the stem has been growing. For example, in fig. 66 the twig shows us five years’ growth if you count the last bud which will grow out to form a shoot.

Fig. 66. Branch of Sycamore, showing leaf stalk (l) with bud (b) in its axil. Scars of leaf stalks (s) and large terminal bud (t) with scars (a), (a¹), and (a²) left by the terminal buds of past years.

The buds which come in the axils of the leaves along the stem may form new leaves, or may develop into side shoots with new stems and leaves. There is another bud, generally bigger than these, which grows at the end of the shoot (t, fig. 66). This has just the same structure as the others, but it will certainly grow out to form a stem and carry on the line of growth of the main shoot, unless it is injured.

The amount that the shoot grows in one year depends on very many things, on the light and warmth it gets, on its food and the growth of its neighbours. Hence, in the growth of different shoots in the same year, or the same shoot in different years, we find very great differences. Sometimes a number of bud scars lie very close together, showing that for several years it had only grown a small amount, while in the years following it may have added very much to its length. In some plants there are little side shoots which never grow much, and always remain quite short; for example, in the larch each tuft of leaves grows on a little stunted stem which represents several years’ growth, and which never reaches any length (see fig. 67).

Fig. 67. Larch, with tufts of leaves growing from short side shoots.

Not only do we get leaves and stems packed away in buds, but the flowers for next year are there also. For example, examine several of the big horse chestnut buds from the outer branches of the tree, and you will be sure to find tiny sprays of young flowers packed away in the hearts of some of them.

There are some quite special buds which we must notice, and which at first sight appear very different from real buds. They have been given a different name, and are called Bulbs. Cut right through a tulip or hyacinth bulb lengthways, and compare it with a horse chestnut bud to which you have done the same. The arrangement of the parts of the two things seems to be very similar. If you examine the bulb in detail, you will find that it is protected on the outside by brown, hard scales, and that the softer leaves within are folded over each other very much like those in the true buds. Now the bud of the horse chestnut is attached to the parent stem—is there nothing corresponding to the stem in the tulip bulb? Look carefully at the base, and you will see a little mass of tissue which holds the scales together (see S, fig. 68); this is the stem, which is short and very much reduced, being unlike a usual stem. There is also one great difference between the scales in the bud and the bulb. In the bud they are rather thin and dry, but in the bulb they are thick and white and very fleshy, and if you test them with iodine, you will find that they contain much starchy food. They form the storehouse of the tulip, and this food will be used by the plant when it begins to grow. In the axils of these thick fleshy leaves you may often find small buds, which will get large and fleshy by next year and form the new bulbs (see fig. 68 b).

Fig. 68. Bulb cut through, showing the overlapping scales (s) packed with food attached to the shortened stem S. B is the bud, which will grow out into the air, and (b) the bud which will form a new bulb next year; (r) adventitious roots growing from the base of the stem.

Sometimes little bulb-like structures grow in the axils of ordinary leaves, for example, in the tiger lily; these drop off when they are ripe, and can grow into whole new plants. They are really half-way between bulbs and true buds.

CHAPTER XV.
FLOWERS

If you have ever noticed a pea-flower fading, you will have seen that from its heart there grows a little green pea pod which ripens till there are full-grown peas in it (see fig. 80); and a yellow dandelion flower turns in the end to a white puff ball which scatters a hundred floating fruits. In fact, almost all flowers which have not been spoiled by the gardeners and “over-cultivated” leave in their place when they die fruits and seeds in some form or other. This gives us the key to the secret of the structure of the flowers themselves. They are the forerunners of the fruits, containing living seed, and their structure and all their parts are adapted in some way to help in the formation of fruit. Now let us examine the flowers, never forgetting that fact.

Fig. 69. Flower of Harebell; (s) sepals; (p) petals.

Let us choose, for example, a harebell. On the outside we find five separate green parts, and if we examine a bud which has not yet opened we shall find that these fold quite tightly over the inner portions of the flower and protect them, as they do in the rose and in almost all flowers (see fig. 69). In this they correspond to some extent to the bud scales, and their special work is that of protection. In all harebells and roses there are five of these parts, but in the wallflower you will find only four, and in poppies two, and so on. There are different numbers of them in the different kinds of flowers. They are also of different shapes and sizes; sometimes each of the five parts is free, and sometimes they are all joined up together to form a true cup, as in the primrose (see fig. 72). These outer green protective parts have a special name, and are called the calyx or cup, while each of the separate parts which makes the cup is called a sepal.

Fig. 70. Buds of the Rose; A with the calyx covering the inner parts, B with the petals opening out.

Fig. 71. Flower of the Rose, with separate petals.

Directly within the calyx we come to the parts which are generally bright and prettily coloured, and which give the chief beauty to the flower. In the harebell which we are examining these parts are joined up to form a bell, but in the rose they are each separate (see fig. 71). In both harebell and rose we find five of these parts, and the same number in the primrose, where you will find that they are joined up at the base to form a long, narrow tube, and then spread out separately like those of a rose. Both in the harebell and primrose, where they are joined up, we can tell the number of parts which go to make the whole bell or tube (and this is nearly always the case in bell flowers), while, of course, where the parts are free it is quite easy to count them, and we find that for each kind of flower their number is always fixed. For example, we find five in the harebell, rose, primrose, and many others, four in the poppy, wallflower, cress, and so on. These parts are called the petals, and in almost all flowers you will find that they are bright and pretty, and stand out from the surrounding green leaves, so that they are easily seen. When the cups or bells hang down they may protect the parts within from the rain, but that is not generally their chief work. The first duty of the petals is to be attractive. You will understand better why this is so after we have gone further into the flower.

Fig. 72. Primrose flower cut open, showing the stamens (s) attached to the tube formed by the petals.

Fig. 73. Flower of Speedwell, with only two stamens (s).

Within the petals, and, in most cases, lying at the base of the bell, you find several yellowish dusty sacs, on fine thread-like stalks. In most flowers they are all free from each other and from the petals, but in the primrose they are fastened to the tube of the petals (see fig. 72). In some flowers you will find a great many of these, as you do in the wild rose (see fig. 71) and the poppy, where there are so many that you can hardly count them. In other flowers there are very few; for example, there are only two in the blue speedwell (see fig. 73). In most flowers the single stamens, as they are called, are very much alike in their structure, and they all have the same work to do. Look at these structures in a tulip or lily, where they are very big, and carefully pull one off and examine it (fig. 74). You will find that it consists of a stalk which we call the filament, with two long sacs at the tip which hold the yellow dust, and which we call the anthers. If you examine a fully blown flower of the tulip or lily, you will find that the sacs split open right down their length and let out a fine yellow powder. This powder is the important thing about the stamens, and is called the pollen. In all stamens you will find the anthers or pollen sacs, while the stalk, which is less important, is not always developed. Sometimes the sacs split right open like those in the lilies, but there are other ways of opening; as for instance, in the rhododendron you will see a little round hole at the tip of each anther, which lets the pollen shake out like pepper out of a pepper-pot.

Fig. 74. Single stamen from Tulip flower; A, anthers, or pollen sacs; F, filament, or stalk of stamen.

Fig. 75. Flower of Tulip laid open, showing the three-cornered central green box containing the young seeds.

Now we have come to the heart of the flower, and find there the most important thing in it. Examine a sweet pea, for example, and you will find in the middle of the flower a tiny green structure very like a pea pod, with a little sticky knob at the tip. In the heart of a tulip you will find a long green box with a sticky, three-cornered knob at the top (fig. 75), while in a buttercup there are a number of these structures instead of one (see fig. 76 s), each of which has very much the appearance of a little pea-pod. Open the pea-pod, or the box of the tulip, and you will find within it a number of very small balls of a clear green colour. These are the young structures which will become seeds when they are older, and they are the most important things in the flower. The green box which protects them is called the carpel in the case of the pea-pod, where there is one space in it. In the tulip you will find that the box is divided into three compartments, and each of these is called a carpel (see fig. 77). You may think of the tulip carpels as being the same thing as three pea-pods joined very tightly together. Some flowers have only one carpel; others have three or five joined up like those of the tulip, while others like those of the buttercup have a very large number of single separate carpels.

Fig. 76. Buttercup flower laid open, showing that there are many seed-boxes (s) in the centre of the flower. R, the receptacle is the swollen end of the flower stalk.

Fig. 77. Carpels of the Tulip cut open to show that there are three spaces with seeds, each division representing a single carpel.

In the pea, tulip, buttercup, and many others, the carpels are in the centre of the flower, above the petals, and attached to the swollen end of the flower stalk, which is called the receptacle, as in fig. 76 R. Other flowers have the receptacle hollowed out like a cup or goblet, and the carpels sunk right in it. When this is the case, we generally find that the sepals and petals lie above the carpels and not below them, as in fig. 78. This is also the case in the rose, where in fig. 70 flower B shows clearly the swollen part below the bud, which is the hollowed receptacle containing the carpels, and the same is true of the harebell (see fig. 69) and many flowers.

Fig. 78. Flower of Cherry cut open to show the hollowed receptacle, R, below the level of the petals, and containing the carpel, C.

What can be the use of the sticky tip that we found on the carpels? Examine the tip of the carpel of a lily which is well open, and you will very likely find some of the yellow pollen sticking to its surface. It is a curious fact that the little structures within the carpels which will become seeds cannot ripen into true seeds unless they are waked up to growth by the pollen grains. The sticky tip of the carpels (or stigma, as it is called) catches the pollen grains and holds them; then they grow down into the carpels and carry with them the nuclei (see p. [92]) that enter the undeveloped seeds. These stir the cells to divide, and after many divisions the embryos are formed and the seeds ripen. Sometimes the stigma has a long stalk which places it in a good position to catch the pollen grains. This stalk is called the style, and is to be found in many flowers (see fig. 72).

The pollen dust is fine and light, and may be carried by the wind on to the stigma, as it sometimes is in poppies, and always is in pine-trees; but this is rather a wasteful way, because the wind blows so irregularly that very much pollen is lost and never reaches the stigma. In order to save some of this loss, and to make the pollinating more certain, flowers have arranged their parts so as to make use of the help of insects. You know that very many flowers have sweet honey in them which the bees like, and come to collect, going from flower to flower to do so. When the bee settles on the flower it gets covered with the pollen dust, and then when it goes to the next flower and walks over it, it is almost sure to leave behind it some of the pollen sticking on the stigma. Of course, in this way also some pollen is lost, but insects are far more reliable than the wind. We now see the use of the bright coloured petals; they help to attract the bees to the flower. The flowers have made the bees and other insects their special carriers of pollen, and they pay the insect with honey, and some of the surplus pollen. Bees generally go from flower to flower of the same kind on any one day’s journey, so that the flowers get pollen from others of their own kind. This is important, for “foreign pollen” (as the pollen from quite different kinds of flowers is called) does not help the young seeds at all.

We have now found a use for all the parts of the flower.

Fig. 79. A, Violet, a two-sides flower. B, Primrose, a circular flower.

There are many special things about flowers which we must leave till later on, but we may just notice now how some are regular, like the primrose, rose, poppy, and so on, which are after the pattern of a circle, and appear the same from whichever side you look. Others, like the violet, larkspur, or sweet pea, are not regular, but have only two sides alike. This difference is very often due to some special structure of the flower in relation to the insects which visit it, and if you examine and compare the two-sided with the circular flowers you will generally find that the two-sided flowers are the more complicated. Some of them become very complicated indeed, like the orchids, which have such strange flowers, and in which the relation between the insects and the flower has become very special.

We must leave these more complicated cases till Chapter XXII., and come back to the simple important facts about the work which all flowers have to do. They must make sure that in some way or other, seeds are formed for the plant. If the flower does not do this, then it is not doing the work for which it was made.

You will find a number of flowers in gardens which do not do their work properly, and very often have no seeds at all, but they are specially cultivated by gardeners to do other things. For the study of the true structures of flowers, it is generally better to examine wild flowers instead of garden ones, which are often much altered by the rather unnatural conditions in which they are made to live.

CHAPTER XVI.
FRUITS AND SEEDS

Fig. 80. A, Pea-flower. B, the same beginning to fade, with the ripening carpel breaking through the keel. C, the same carpel much enlarged, the petals and stamens quite faded.

Within the flowers we saw, protected and shut in, the carpels or seed-box, within which are the very young structures which will become seeds. Now let us watch them develop. In such flowers as the sweet pea, for example, in summer-time, this will not take very long. Mark a special flower, and watch it each day; you will find the little green pod will gradually grow bigger, till it splits away the petals which are beginning to wither, and pushes out between them. As the pod gets larger you can see the seeds within growing too, if you look at the pod carefully against the light. The stigma does not grow any further, as its work was finished when it had caught the pollen grains. After a time the petals and stamens drop right away, and only the calyx remains; it does not grow very much, but it keeps fresh and green for some time, as it has still to act as a cup to hold the pod. It only takes a few days for these things to happen, then till the pea pod is quite ripe may take a week or two more. The pod continues to grow and turns yellowish brown and dry, then one day when the sun is warm you may see and hear it split open suddenly down its central ridge, and shoot out the brown, dry seeds. Then the work of the flower is quite over, and the seeds have started to make their own way in the world.

Fig. 81. A, ripe carpel of pea or “pea pod.” B, pod suddenly split and twisted up, scattering the seeds.

Let us pick a nearly ripe pea-pod and examine it; it is the ripe carpel, with several ripe seeds in it, and together they form what is called a fruit. In the case of the pod the “fruit” itself is a dry pea-pod husk, but in other plants the fruits may be very different. Examine a marrow, for example. Watch it in the course of its growth, if possible, and you will find that the marrow flower is one of those with its seed-box below and outside the calyx and petals. As the marrow ripens this swells with the food stored in it, and the many growing seeds, till the flowers are only small shrivelled structures at one end. If you then cut the ripe, or nearly ripe, marrow fruit across, you will find that its wall is very thick and fleshy, and that the many seeds are buried in a soft pulp. The melon shows us just the same thing. Such fruits seldom split suddenly to shoot out their seeds (though some foreign ones do); they depend more on animals which may eat them and so scatter the seeds about.

In all cases it is better for the plant to have the seeds scattered so that they do not sprout too near together, but have room enough to grow without crowding each other out.

In the pea and marrow there are many seeds, but there are large numbers of fruits in which we find only one. For example, in plums, cherries, and peaches we have a fleshy outer fruit-case with a stony lining covering over one large seed. Such fruits do not open, for there is only one seed within, and so the fruit is scattered whole. These fruits nearly always get scattered by animals, for the flesh is very sweet and attractive to eat, and then, as a rule, they get rid of the stone (which contains the seed) at some distance from the parent.

Fig. 82. Cherry fruit cut open, showing the flesh (f), stone (s), and seed S.

Sometimes we find a number of fruits just like the cherry clustered together, only instead of each of them being large, they are all very small, so that the whole cluster of fruits may be the size of a single cherry. This is the case in the common blackberry and the raspberry, where each of the little fruitlets really corresponds to a cherry.

Then there are many fruits which belong to quite a different class, and arrange to scatter themselves by the help of the wind, such as the fruits of the dandelion, thistle, and many others, which have light “parachutes,” and therefore blow away with the least puff of wind when they are ripe and dry (see fig. 83).

Fig. 83. A, head of Dandelion fruits, with most of them scattered. B, single Dandelion fruit.

Other fruits like the sycamore have big side-wings which catch the wind as they fall, and get twirled for some distance. In these cases each of the separate parts which flies is really a fruit, only in the case of the dandelion, thistle, and many others, each of these fruits contains only one seed, and the fruit itself is so small and dry that we get into the way of speaking of the whole fruit as a “seed.” This is not correct, however, because even though there is only one seed present, yet it is surrounded by the dry remains of the ripe carpel, and is therefore a fruit.

Simple seeds which have wings are rather rare, but we find them on pine seeds (see fig. 125), and the seeds of the willow herb are covered with a number of silky hairs, which make them so light that they fly in the wind. It you watch a spray of willow herb ripening, you will find that the old carpels, or fruits, split up into four parts and let out a number of fluffy white seeds. These are true flying seeds (see fig. 84).

Fig. 84. Fruit of the Willow herb, opening and allowing the flying seeds to escape.

Other seeds get scattered by the wind although they do not fly. For example, in the poppy the fruit is the hardened ripe carpels which have become quite dry, and together look like a little round box, within which there are many tiny dry seeds. When the box or capsule is quite ripe openings come in it, just below the projecting top, and then, when the weather is dry and they are open, a strong wind may bend the stalk of the fruit and shake the capsule strongly. The seeds come scattering out like pepper from a pepper-pot, and may get carried some distance from their parent plant (see Plate II. and fig. 85).

Fig. 85. Ripe Poppy capsule, showing the little pores at the top which let out the ripe seeds when the capsule is shaken.

Some fruits are covered with spines and hooks, which catch on to the wool of animals, and so get carried quite a distance before they are dropped. This gives the seedlings a good chance of reaching a new spot where they can grow away from the parent, and so not be too crowded. Well-known fruits of this kind are the burs, which stick tightly to one another with their dozens of little hooks, the “bur” being really a cluster of many fruits together. Simple fruits of the same kind are the bidens, each with its two long spines, and the small fruits of the goose grass, which are covered with the finest hooks.

Fig. 86. A Bur, which is a cluster of hooked fruits.

Fig. 87. Simple fruits: (a) of the Goose grass with its hooks; (b) the Bidens with its harpoon-like spines.

Fig. 88. Strawberry. Each of the little “seeds” is a whole fruit, and the “flesh” the swollen receptacle.

Quite a special kind of fruit is the strawberry, which, as you know, has a thick fleshy pulp covered with a number of small, yellow “seeds.” In reality, each of these “seeds” is a whole fruit, and the thick flesh which we eat is the swollen end of the flower stalk which we call the “receptacle.” Therefore a strawberry really consists of a large number of fruits and a piece of stalk which is altered to form the fleshy, attractive mass which induces birds and people to eat the whole, and so scatter the little dry fruits.

There are very many other kinds of fruits which all have special devices to make sure that their seeds are scattered, and all proper fruits have seeds in them. But, just as we found that some garden flowers are grown only for their beauty, and do not set any seed, so we find that some fruits are grown specially without any seeds, such as bananas and some oranges. Such fruits are the result of our liking to eat the soft, sweet pulp without the trouble of the seeds, but such fruits are of no use to the plant.

Now let us look at the structure of the ripe seeds themselves, and see how they are fitted to go out alone into the world prepared to make a new plant. Seeds are all very much alike in the important points of their structure, although they vary much in the shape, size, and colour of their parts. We already know what beans are like from our careful study of them at the beginning of our work (see Chapter III.), and beans show us particularly well all the important parts of a true seed, so that we may take them as being typical of one large family of flowering plants. The maize embryo (see p. [10]) is typical of the rest of the flowering plants. In the ripe seeds of both of these groups (you should examine them again if you have forgotten any of the facts) we find that the important thing is the baby plant, which is supplied with food and protected by two seed coats, till it is time for it to grow out and form a new plant like its parent.

Fig. 89. A, outside of Bean; (h) black scar showing where the bean was attached to the pod; (r) ridge made by young root; B, bean split open; (n) nurse leaves; (p) embryo; (a) scar where the embryo was separated from the nurse leaf on that side.

Fig. 90. A, outside of Maize, showing the embryo (e) on one side; B, sprouting, showing the root (r) and shoot (s); C, the same further grown.

CHAPTER XVII.
THE TISSUES BUILDING UP THE PLANT BODY

Fig. 91. Two cells from plant tissue. (c) Living contents; (n) cell nucleus; (v) spaces filled with sap; (w) wall of cell (much magnified).

In our study of plants up to the present, we have only looked at their structures from the outside. We have examined the form, uses, and life of the parts of their bodies without looking for the details which might answer the question—“How are they built up?” Just as a house as a whole has a definite form, with rooms, and doors, and windows, each with their definite form and use, and at the same time every one of these things is built up of small separate bricks, tiles, pipes, and pieces of wood: so we find that the whole plant is composed of a number of definite parts, which are themselves built up of tiny individual parts, which we may take to correspond with the bricks of a house. Of course, they do not do this completely, for a plant is a living thing, and is far more complicated than a house, and each of the tiny individual parts is also a living, growing thing. These little building structures are called cells both in plants and animals, and they are so very small that you cannot study them fully without a microscope, and that is a very complicated and expensive thing, so we will leave it alone and only study what we can see of the structure of plants without it. Try, however, just to see a few cells under the microscope, so as to know what they are like. A typical cell has a wall, within which is the actual living substance, a clear, jelly-like mass, which contains many granules of food and stored material. Within this living substance is a more solid mass of still more actively living substance, which is called the nucleus. Cells like these, or cells which were like these when they were young, and which have become modified for special work, build up the whole plant body (see fig. 91).

Fig. 92. Piece of thin section across Water-lily stem, showing mesh-work tissue seen with a magnifying glass.

You can get a good hand magnifying-glass for several shillings, and with this and a very sharp knife, you can find out something of the structure of the insides of plants, even though most of the cells are so small as to be out of sight except when looked at through a microscope.

Let us first cut as thin a slice as possible across a water-lily stem, and put it on a small piece of glass and hold it up to the light. Examine it with the magnifying glass, and you will see that it is not a solid mass of tissue, but that it is built up of a fine network like lace, with quite large spaces between the threads (see fig. 92). These spaces are air spaces, and the fine lace-work threads are meshes built up of single rows of cells, which you may be able to see if your glass is a good one. Cells may be packed loosely like this, or they may be in more compact form something like a honeycomb, as you may see in the pith of an elder twig and many other stems. You can crush these soft cells between your fingers, and we cannot imagine that they could build up the hard, firm branches of trees.

Now examine the stem of a seedling sunflower, by cutting a very thin slice across it; you will see in it a ring of strands where the cells are smaller than those of the soft tissue and also much more closely packed (see fig. 93). Then cut a thin slice longways down the stem, and you will see that these more solid strands are the cut ends of long strings of such tissue which run through the stem. The cells which build up these strings are not quite ordinary cells, but are exceptionally long, like water-pipes, and they have thickened walls. These cells do the carrying of water and liquid food up and down the plant (see fig. 94).

Fig. 93. Piece of the stem of a seedling Sunflower cut across, showing strands of “water-pipe” cells.

Fig. 94. Piece of stem cut across and then split lengthways, showing the strands of thicker “water-pipe” walls.

You can see that the water travels up these cells if you cut across a stem near the root and place it in a little red ink. After a few hours if you cut a section several inches from the bottom of the stem you will find that these strands are coloured red by the ink which has passed through them, while the rest of the stem is very little coloured, or quite colourless. This shows us that these strands are the special water-pipes of the plant.

Fig. 95. Cross section through a Lime twig three years old seen with a magnifying glass.

Large numbers of such cells closely packed together, and with some other hard cells between them, make up the wood in woody stems. Cut across a small twig of lime or oak and examine it with your lens. Outside is the brown bark, then within that some green cells and a little soft tissue, while most of the stem is made up of a mass of hard wood cells, among which you can see some of the larger water vessels distinct from the rest. All this hard tissue really corresponds to the joined up separate strands which we saw in the sunflower stem (see fig. 95). Trees like the lime and oak, which live for a long time, grow for a certain amount every year, and each year they add a ring of wood to their stems. In old stems you can see clearly the rings of wood which have been formed by each year’s growth. This is another way of telling the age of the stem, and you should compare your results from this method with those you got from counting up the bud scars (see p. [75]).

Leaves, as you know, require much water, which comes to them up the stem through the “water-pipes.” You saw already the course of the water-pipes in leaves, for they are the “veins” which we found sometimes make a complete network, and sometimes run parallel in the tissue of the leaf. If you put a leaf stalk in red ink, you will see that the veins are connected with the water-pipe strands in the stalk, for they will both get coloured by the ink as it passes along them.

Just as in animals the whole body is covered over with a skin, so in plants we find a special outside sheet of cells, which protect the inner tissues and form a thin skin. You can get this off very well if you break across an iris leaf, and pull along the thin, colourless layer on the outside. If you examine it with your lens, you may perhaps see something of the mosaic-like pattern of the cells which build it up. You should certainly see that it is colourless, although the tissue of the leaf beneath it is quite green.

On the large branches of trees and the bigger plants, we do not find this delicate protecting layer, but instead there is a thick brown cork. When the cork layer gets very thick it splits irregularly as the tree grows too big for it, and so forms a rugged bark. The cork layers have much the same duty as the fine skin, only they are thicker and stronger, and more suited to hold out through the winter. You know already from daily life the practical use of cork, for you put it into bottles to keep the liquid in the bottle and the damp and dust in the air from entering. Just what the cork does for the bottle, the sheets of cork wrapping round the branches do for the plant. They prevent it from being dried up by cold winds, and they keep out the heavy rains of winter which would injure it. Roots have a cork coating also when they get old. As you may remember, it is only the tip of the root which can absorb water for the plant, so that in the young part of the root a cork layer would be very much out of place, and you will never find it there. You will find instead the little delicate root-hairs, which absorb water and pass it on to the older parts; these old parts do no more absorbing, they are only the water carriers and food storers, and so have no hairs and are protected by a layer of cork.

As we found before, plants breathe in air like animals, and you may ask how they can do this when they are covered with their thick air-tight layers of cork. Examine a fairly old elder twig, and you will see all over its brown skin numbers of darker brown spots. If you look at these with your magnifying glass, you will see that they are quite spongy and soft. They are the special entrances for air, and are the breathing spots or lenticels (see fig. 96). They are to be found in all corky stems, although they are not always so easy to see as in the elder.

Fig. 96. Piece of Elder twig, showing the breathing pores in the bark.

On the leaves and stems of many plants you will find a large number of hairs. In some cases there are so many as to make the whole plant quite woolly, like the mouse-ear leaves. These hairs are protective, and keep the leaf warm and dry, and in some cases may shelter it from the sun. Hairs may consist of one cell, or several in a row, or of cells which are branched in a complicated way. Certain hair-cells protect the plant by stinging, as you can see if you watch a nettle-leaf with your magnifying-glass, and then rub your finger along it, only touching the hairs. You will find that it is they which sting you, and not the leaf itself.

Now we have found several kinds of tissues in plants, the skin and cork covering all over and protecting the rest; the central vessels or water-pipes, corresponding to the veins and arteries of animals, the soft white ground tissue, which in some stems may be very loosely packed, and the soft green tissue in the leaves and young stems, which we found was the food-manufacturing part of the plant. There are also strands of simple strengthening tissue, both by the water-pipes and in separate bundles in the soft tissue; these we may take as representing the bones of animals.

We have noticed (Chapter VIII.) that plants are sensitive to light and bend towards it, that they feel heat and cold, and that the stem and root seem to know when they are growing in the right or wrong positions, and bend accordingly. We know that we ourselves and the animals recognize such things by the help of nerves which carry messages to the brain. But where is the brain in plants, and the nerves? No true nerves have been found in plants, and it seems as though different parts of the plant were specially sensitive without there being any “brains.” So that we cannot speak of a central nervous system in even the highest plants as we can in the animals. In this respect they are built on quite a different plan from animals.

PART III.
SPECIALISATION IN PLANTS

CHAPTER XVIII.
FOR PROTECTION AGAINST LOSS OF WATER

If you go along the lanes and in the gardens in the height of summer when it is hot and dry and the sun beats on the plants all day, you may see them beginning to wither for want of water. The roots are not able to find enough moisture in the soil to supply the leaves, which, being in the hot air, continue to transpire away the water resources of the plant, so that in the end each of its cells must suffer and the whole become limp and droop. This happens because the ordinary green plants of our country make no special preparation for such dry weather. Our hot season is short, and even in the summer we have frequent showers which keep the soil moist enough to provide the plants with water from day to day, so that they have not become accustomed to long periods when there is no prospect of rain.

Fig. 97. A Cactus with needle-like spines for leaves, and a thick green stem.

Compare one of our usual green plants, a sunflower, for example, with such a thing as a cactus, which you may get growing in a pot of dry sand. The cactus is able to withstand the hottest sun for days, though it gets very little water, and sometimes apparently none at all; yet it does not wither, but grows, and may bear the most lovely flowers. From travellers we learn how the huge cactus plants grow in dry and stony deserts, standing every day in the blazing sun. Such is, of course, their home, and they are used to it; but how is it that they are able to flourish under conditions which would kill one of our own green plants?

Let us look at their structure and see in what they differ from a usual plant. First, they have no green leaves, for these have developed into spines (see p. [62]), while the sunflower has many large ordinary leaves.

You will remember that the surface of leaves is continually giving off water from its many pores. When a plant has a number of big leaves this transpiring area is large, while when it has no leaves at all, but a thick, green stem instead, then the amount of surface from which water vapour is being given off is very much reduced, even though there may be about an equal quantity of actual tissue in the two plants. You can see that this is the case if you take a ball or thick block of dough and roughly measure its surface, then roll it out till it is fairly thin and measure it again; you will see that the thinner you roll it the more surface there is; all the time, of course, the amount of actual dough remains the same. So that of two plants of the same bulk, the one with broad, thin leaves will expose the most surface to the air, and so lose more water than one with very thick leaves or none at all. The latter would therefore be better fitted to live under dry conditions.

But, you may say, leaves have a definite work to do; how can the plant live without them? In the cactus the thick stem is green and does the work of food building; naturally it cannot do so much for the plant as many big leaves could, but it does enough to allow it to live and grow slowly and surely for many years, though it cannot grow in each year nearly at the same rate as can the sunflower. If you cut through the stem of a cactus you will find that its skin is very thick and tough, and this thick coat protects the plant against the fierceness of the sun far more completely than the thin skin of a sunflower does. At the same time, the tissues of the two stems are different; the sunflower is hollow and delicate, but the cactus is very thick and juicy, and each cell contains much gummy stuff which has the power of holding water strongly. So that we see in many important points the structure of a cactus is different from that of a usual green plant, and is specially suited to the dry conditions of the desert.

Many desert plants are built on the plan of the cactus, but there are also others which are not at all like them, and yet they are able to live in deserts and very dry places. It you examine them, however, you will find that they all have some special way of protecting themselves from being dried up. Some of them have hard, dry, woody stems, well protected by corky layers, and they only put out green leaves in the rainy season, and lose them directly the hottest weather begins. Others, which grow from seed every year, learn to sprout, flower, and fruit very quickly while there is some moisture, and they form well-protected seeds, which wait till next rainy season. One very curious desert plant has only two leaves, which last it the whole of its life, and which are very hard and leathery. There are endless varieties of things which the plants may do to protect themselves from being dried up, and we can only look at a few special examples.

To find plants growing in desert places we do not need to go out of England, because from the point of view of the plant, one which is growing on a dry rock or on a patch of bare dry sand, is really growing in a little desert. For it the supply of water is the chief problem, even though we never get hot tropical sunshine in England. Look, for example, at the plants growing on the sand dunes which are very like deserts in appearance, and the plants on dry walls, or on the “screes” of broken rock at a hill foot; they are all growing in deserts.

In many cases plants growing in such positions have small thick leaves, nearly round, or shaped like sausages, so that they have much water-storing tissue in proportion to a small transpiring surface. This is the case in the stone-crop (see fig. 98) and the house-leek, where each separate leaf has followed the same principle as the cactus stem, and exposes relatively little surface to the air. Such plants frequently have very long roots, which penetrate deeply between the cracks of the rocks and find hidden sources of water.

Fig. 98. Thick fleshy leaves of Stone-crop.

Other plants, instead of having leaves of this type, have exceedingly small leaves which may soon drop off, while the stem is green and does some of the food building. Small leaves are assisted by the green stem in gorse (fig. 99), which often lives in very dry places, though it can grow equally well under usual conditions.

Fig. 99. Gorse, with green stem which does the work of leaves.

Many plants roll up their leaves when it is dry, so that the surface with the transpiring pores is on the inside, and protected by the outer side with its hard skin (see fig. 100). In damp weather these leaves unroll, and do all the work they can. Leaves like this are to be seen in many of the grasses, particularly those growing on sand dunes and moorland; while a number of the heaths and heather do the same thing to protect their transpiring surfaces.

Fig. 100. Leaf of the Sand-grass. A, rolled up; B, open. (a) and (b), sections across the same.

You will find that in nature, water is one of the most important things in the surroundings of plants, and in their struggles to get it and keep it they have changed their forms in many ways, and in some cases have become extraordinary-looking creatures as a result.

CHAPTER XIX.
SPECIALISATION FOR CLIMBING

If you go into a wood, or even a thicket, in summer, you can see how the leaves of the big trees make, what is for us, a delightful shade. But look at the ground under these tall trees, at a place where they are growing thickly together, and you will find that there are very few plants below them, and that the earth is almost bare except for dead leaves, twigs, and a few mosses. In deep pine-woods there are great patches without even the mosses, where are only dead pine-needles and some toadstools. You can well understand, when you remember how very important light is for the plants, that it is too dark for them to grow under the heavy shadow of thick trees. Even in gardens you may see how the tall, quickly growing plants kill off the smaller ones beneath them.

When many plants are growing together, it is easy to see that the taller ones get most light, but if a plant grows very tall it requires a strong stem to hold it up right, and that means the building of a large amount of wood which takes a quantity of material, so that the growth must be slow and costly.

Some plants, however, have learned to grow up into the light without building a firm stem for themselves, because they use instead the support of other plants, and especially of trees. You must often have noticed in a wood great sprays of honeysuckle sprawling high up over the trees; sometimes one of the festoons of honeysuckle may lie over the branches of several trees, and so get into the best positions for the light. The Travellers’ Joy, or white clematis, grows all over the tall hedges, and may sometimes completely smother a young tree, so that one can see nothing but the leaves and light green and white flowers of the clematis. Then, too, there is the ivy, which you know may sometimes grow up trees to a very great height, covering over the leaves so that the whole looks like a giant ivy bush. These plants all get their support from trees, which have built themselves strong stems. Pull down a big branch of honeysuckle or Travellers’ Joy from the supporting tree-trunks, and you will see that it cannot remain upright but falls limply to the ground. It is true that these plants have some wood in their stems—sometimes clematis and ivy may have woody stems several inches thick, but they are never strong enough to support the weight of the crown of leaves and branches. By clinging to others in this way these plants can economise much building material and reach the light far quicker than they could do otherwise.

If you examine their wood, you will see that it is not quite like that of usual plants. Cut through the stem of a clematis which is about an inch thick, and even before you look at it with a magnifying-glass you will see how very loosely built the wood is, with wide rays of soft tissue and very large water vessels. It is not built for strength and support, but merely to carry supplies of water up to the leaves, for although these plants use trees as supports, they do not get anything more from them, and must supply themselves with all else they need. You may often see that the central part of the wood is not in the true centre of the stem, but is pushed to one side, and the rings of the year’s growth are very irregular, being much more to one side than to the other. This is because they lean against the supporting branches, and so must grow chiefly on the side away from them. Sometimes as the ivy grows right round the support, it will grow more, first on one and then on the opposite side of its stem, and so the centre does not remain in one place, but shifts round.

The other parts of these woody climbing plants are but little out of the common. They have merely learnt to economise their own stem-material, and at the same time to reach a good position in the light, so that it is in their stems that we find their chief differences from usual plants. The honeysuckle and clematis have no special climbing organs, but the Ivy has clusters of adventitious roots which come out from the back of its stem, and hold it on to the support (see p. [56] and fig. 101).

Fig. 101. Adventitious roots growing out from the stem of Ivy between the leaf stalks.

In climbing plants in which the above-ground parts live only for one year and then die down, we do not get a woody stem. Such soft green plants as the hop and convolvulus, for example, are entirely dependent on others for their support. They have specially sensitive tips to their stems, which feel the support and definitely twine round it in a close spiral, which clings ever closer to the support as they grow (see fig. 102).

Fig. 102. Soft twining stem of Convolvulus.

Climbers of this kind have only modified their stems; the rest of their parts are not in any way specially altered by this habit.

Some plants which sprawl about on others hold themselves up by the power of clinging and twining in their leaf-stalks, for example, in the nasturtium we find that the plant is held up entirely by the leaf stalks, which catch on to anything in their way (see fig. 103).

Fig. 103. Nasturtium stem held up by the support given by the leaf-stalks, which cling around any suitable prop.

Very many plants which depend on others for support modify their leaves, or parts of leaves, to form sensitive tendrils which twine quickly round any prop they can find, and thus hold up the stem (see fig. 104). The young tip of the stem continues to grow upwards, the next young leaves unfold their soft green tendrils which twist round a support directly they feel it, and so the plant goes on growing higher and higher. You can see the fate of a pea-plant which does not find supports, by growing one in a big pot all by itself. It will grow upright at first, but it will soon have to creep along the earth and fall over the edge of the pot, for its stem is not strong enough to support its own weight.

Fig. 104. Sensitive tendrils of the Pea. (t) tendril at the end of foliage leaf, (o) ordinary leaflets.

In vines and marrows we also get tendrils, but they are not modified leaves, but special branches which have become sensitive.

In some plants the sensitive tendrils do not twine, but instead form little sticky suction pads at their tips whenever they come in contact with the support, and these hold the tendril very firmly on, as you can see in the ampelopsis, which grows right up the walls of houses. If you look under the thick covering of leaves, you will find these tiny padded tendrils clinging tightly to the wall (see fig. 105). This is the reason that the ampelopsis grows so well up the walls without being held up artificially.

There are many other things you may find out about climbing plants, but you will have seen enough to be able to look for more for yourself, and to understand how it is that the climbing plants can reach such a great height so quickly. They have learnt to avoid the trouble and expense of building strong supporting stems for themselves, and by getting their support from others, they are able to grow quickly out into the good positions for the light which they could not otherwise have reached.

Fig. 105. Ampelopsis, which supports itself by the little suction pads developed at the ends of the tendrils.

CHAPTER XX.
PARASITES

We call a plant or animal a Parasite when it does no food-building for itself, but adapts its whole structure to obtain and use the food made by the work of other plants or animals. Plant parasites generally attach themselves to a “Host” plant so closely that they suck their food from it, and sometimes remain with it till they have finally killed it, and so have destroyed their only source of food and means of life.

Among plants, most of these degenerate creatures belong to the group of Fungi. The rust and smut on wheat, the mildew on fruit, and nearly all the thousand spots, blemishes, and diseases of cultivated and other plants, are the result of the parasitism of some members of the family of fungi. Plants which prey like this on others are without very many of the characteristics of true plants; they become colourless, losing their green substance, and with it all power of building food for themselves, so that they are quite dependent on the host plant, without which they must ultimately die.

Fungus parasites, of which there are many thousands, have become so specialized that they are quite a study in themselves, and we will leave them for the present and follow the history of a few of the higher plants which have taken to this mode of life.

Fig. 106. Dodder plants growing over Clover. (a) clusters of Dodder flowers.

One of the most completely parasitic of the flowering plants is the dodder, which you may often find growing on clover. In fields of clover sometimes there are colonies of dodder, which live together and kill the clover in great patches so that it almost looks as though it had been burnt. Dodder grows on other plants, such as gorse, as well as clover, and even on nettles. If you find a plant of dodder you will see that it seems to consist of nothing but fine, white or pinkish threads, twisted round and round the clover stems and hanging in festoons over them. Pull off these fine threads carefully, and you will find that at intervals along them there are little sucker-like pads which hold the dodder quite firmly on to the plant on which it is growing. If you cut through the middle of one of these pads and the clover-stem while they are still attached, and look at the cut with your magnifying-glass, you will see how the tissue of the dodder pad enters right into the tissue of the clover stem (see fig. 107). These pads act as suckers for the dodder and draw from the clover all the ready-formed nourishment that the dodder requires, so that it has no work to do in food building. It has no roots because it needs none; the suckers act as roots in getting all the water and also the manufactured food the plant uses; for the same reason it requires neither leaves nor green chlorophyll, and its body is only a colourless or pinkish mass of thread-like stems and sucker pads.

Fig. 107. Section, A, across the Clover stem, with the Dodder D attached. S, suckers of the Dodder, entering the Clover.

There is one thing, however, that the clover plant cannot do for the dodder, and that is, make its seeds. When the clover builds seeds, then they are clover seeds and will grow up as new clover plants. The dodder must build its own seeds if dodder plants are to grow from them. That is why we find growing out from the simple reduced thread of a stem, relatively large tufts of flowers (see fig. 106), which are very little different from usual flowers and which form seeds. The dodder belongs to the same family as the convolvulus, and though its flowers are small, if you examine them with a magnifying-glass you will see that they are very much the same in structure as those of the convolvulus.

When the young dodder plant grows out from the seed, it is a simple little thread with no leaves, and it keeps on growing at the tip, which it moves round till it feels some suitable host, then it quickly fastens on to it and lives on its food.

This is the general history of all kinds of parasites, for when any living thing ceases to use its structures and becomes a complete parasite it loses nearly all its parts, as there is no longer any need for them. So that parasites tend to sink to a lower level of development simply as a result of their way of living.

A plant which is largely a parasite, but yet does a little work for itself, is the mistletoe (see fig. 108). Its leaves are greenish, but not the true healthy green of a hard-working plant. If you can find a bough of mistletoe growing on an oak or apple tree, you will see that it has no root in the earth, but grows out of the bough of the host tree. It has sucker-like roots at the base of its stem, which go right into the stem-tissues of the host and get much nourishment from them.

Fig. 108. Young Mistletoe attached by its sucker-like roots S to a twig of apple A, split open.

In the winter, when the flow of food is very slow in the host, it is likely that the mistletoe does some of its own food building in its yellow-green leaves, which would be exposed to the full light, as the host’s leaves would have fallen away. The mistletoe has soft, white fruits which are scattered by birds, and as they are very sticky, they hold for some time on to the branch where they are dropped, and there the seedling sprouts and fastens itself on to the tissues of the host, growing every year with its growth.

Fig. 109. P, parasite attached to the root R of a host plant H (which is the Ivy). A is the host root on the other side of the parasite.

Quite a number of plants which grow in the ground attach themselves with suckers to the roots of other plants, from which they get all their ready-made food. Plants which do this are generally colourless or brownish yellow, like the broomrape, which has only whitish leaves which cannot do the proper work of leaves (see fig. 109).

Then there are several plants which are partly parasitic, but which you would never guess were anything but ordinary plants. For example, the little eyebright with its green leaves, which do most of the food-building, is yet partly parasitic. If you very carefully get out a whole plant with its complete roots (this is rather difficult to do, and you must not pull it hastily, or you will break the connections), you will find that there are tiny suckers on them which connect them with the roots of the plants which are growing near. So that the eyebright gets some of its food ready-made from the neighbouring plants. The meadow cow-wheat does the same thing, and so do the lousewort and several others; but they are not complete parasites, for they are green and do a lot of work for themselves, even though they are not quite self-supporting, and tap the supplies of other plants to some extent.

Among flowering plants, parasites are not common. We see in plants like the eyebright and cow-wheat, which do a little thieving, that the results are not very serious, and they are little altered by their habit. In those which are entirely parasitic, however, like the dodder, the result is the loss of nearly all the organs of the plant except the flowers, which have to be kept in order to build seeds.

CHAPTER XXI.
PLANTS WHICH EAT INSECTS

As a rule, plants are the sufferers and are eaten by animals, but there are cases known in which this state of things is reversed; the plants catch and devour the tinier animals and small insects such as flies. But, you may ask, how can they do that, for the insects move so quickly, and the plants are fastened by their roots to one spot. Just as a spider builds a web and then waits quietly beside it till the flies are caught, so the plants build traps which catch the unwary insects. There are not very many plants growing wild in England which do this, but there are one or two that you might be able to find.

Fig. 110. Plant of Sundew, showing the round leaves covered with tentacles.

There is the sundew, which grows among bog-moss in wet, swampy places at the edges of lakes, or on the wet patches on hillsides. It is fairly common in such places, a little distance from big towns, but it does not like smoke, so that it will not live within a few miles of London, Manchester, or any big smoky town. It is a small plant with round, reddish-coloured leaves, covered over with little fingers or tentacles each with a sparkling drop of sticky moisture at the end, so that even in the heat of the day when all the dew is dried up, the whole plant looks as though it were spangled with tiny dew-drops. Perhaps it is this cool, sparkling appearance which attracts the insects to it, but when once a fly alights on one of the leaves, its fate is sealed. The tentacles with their sticky tips bend over one by one till the fly is quite covered in by them and cannot get away. It dies, and is digested by the juices given out by the leaf, which are very much like the digestive juices of animals.

Fig. 111. Single leaf of Sundew, with the tentacles closing over a fly.

You can watch the movement of the tentacles very well if you drop a minute piece of meat or white of egg on to the leaf. They will close over it one by one till it is quite shut in, and when the egg is all digested, they slowly open out again. The time that this takes depends a little on the health of the plant and the time of the year, but generally all the tentacles are bent over in a few minutes. The digestion takes longer, of course, at least several hours and often more, partly depending on the size and nature of the piece of food. The sundew leaves contain chlorophyll and do some of the usual work of leaves, but the plant gets much of its nourishment from the insects it catches.

Fig. 112. Butterwort, showing the rolled leaves which catch flies and other small insects.

In the butterwort there is a different arrangement for catching its prey. You will find its little clusters of broad, spoon-shaped, yellowish-green leaves growing in marshy places and beside streams in hilly districts. In the spring one or two lilac flowers on long stalks come up from the centre of the group of leaves. The leaves of this plant also act as insect traps; they are covered with little sticky glands, and when an insect settles on them, the edge rolls over and shuts it in, keeping it there till the juices given out by the glands have digested all that is worth digesting, when the leaf unrolls again, and the remains of the feast are washed away by the rain.

Fig. 113. A piece of leaf of Bladderwort showing the bladders on the branches.

There is one more animal eater which you must try to see, which grows in the water of slow-running streams and in ponds. It is the bladderwort, on which we find very many tiny bladder-like structures on the finely divided leaves under the water. The bladders are built on something of the same plan as a lobster pot, with bristly hairs pointing into the entrance, across which there is a little flap, which makes it quite easy for the very minute animals living in such abundance in the water, to swim into the bladder opening, but extremely difficult or almost impossible for them to swim out again (see fig. 114). So there they must finally die, and their nourishing juices are absorbed by little compound hairs, many of which are developed on the inside of the bladder.

Fig. 114. A single bladder of the Bladderwort, much enlarged, showing the pointed hairs and the flap at the opening.

In the tropical countries there are many kinds of “pitcher plants” with wonderful soup-kettle-like pitchers which catch insects. You may be able to see these plants in a big greenhouse, and should certainly find them in every botanical garden. Notice how large the pitchers are, and that they are really modified leaves which have become different from the other leaves of the plant because of their special work. They generally contain a considerable quantity of water as well as the flies they have caught, and are really “stock-pots” which keep the plant supplied with nourishing, ready-made food in addition to the food which it builds for itself in the green leaves.

Fig. 115. Pitcher leaf of Nepenthes, which acts as a “soup-kettle.”

Though these plants have specialised themselves to catch and use animal food, still there are not very many plants that do so, and the old fairy tales about trees with branches which caught men and devoured them, as a sea-anemone catches and devours its food, are only fairy tales, because no such plants exist.

CHAPTER XXII.
FLOWER STRUCTURES IN RELATION TO INSECTS

The relation between flowers and insects is one of mutual help and advantage, and therefore is quite different from that in the cases where the animals eat the plants or vice versa.

When we examined flowers in general, we found that the insects do a very important work in carrying the pollen from flower to flower, and that their structures are arranged to attract insects and to make it easy for them to get covered with the pollen of one flower and leave it on the next. If we look at the details in some of the flowers, we shall see how elaborate their structures may be, and how carefully they are planned to make sure that the bee gets the pollen on its body and carries it with it to the neighbouring flowers.

Fig. 116. Circular flower of Rose, with many stamens in the centre.

In the simple circular flowers, such as roses, poppies, and lilies, the bee can enter freely from any side that it chooses, and it generally goes straight to the centre. Many of these simple flowers, therefore, have large numbers of stamens which stand up in a crown in the middle, so that the bee must touch and stir some of them as he dives in the centre for the honey.

Fig. 117. Slightly two-sided flower of the Foxglove, with the petal tube cut open to show the four stamens bending to the front.

In others which are nearly circular, there is a little difference between the back and front of the flower, and the stamens are so placed that the visiting insect must touch them. For example, look into the bell of a foxglove, where you will find only four stamens, but they are bent so that the anthers together form a kind of platform in the front of the flower, over which the bees must pass as they enter (see fig. 117). Frequently the stamens bend in this way towards the front of the flower, and in many cases the whole flower becomes quite definitely two-sided, with a front and back, and a special place for the entrance of the bee. This is the case with the violet, pea, monkshood, and many others (see fig. 118).

Fig. 118. Two-sided flowers: A, Monkshood; B, Violet.

When flowers have this form, you frequently find that the number of stamens is quite small, seldom more than ten, and often less.

A plant of this kind very interesting to watch is the yellow gorse. If you can get up and sit by a flowering bush from about half-past five to seven one sunny morning, you will be able to learn a great deal about the doings of the bees and flowers.

Fig. 119. (a) Flower of the Gorse after the insect’s visit, showing the inner parts exposed; (b) young flower nearly ready to be visited.

First examine a flower so that you know how it is arranged. At the back lies the big petal, or “standard,” as in the pea; there are two side wings, and in the front the two petals close together forming the “keel.” The two-sidedness of this flower is very well marked. Inside the keel you will find ten stamens, all joined to form a tube except the back one, which is free, and inside them lies the carpel with its curved style. When the stamens are ripe they are so fitted that they lie inside the keel of the petals in a bent form, and when they are pressed from above they fly out with a little explosion and scatter the pollen dust about. Now watch a bee alighting on the flowers; he presses the two front petals with his legs to open them to get at the honey, and the stamen explosion covers him all over with pollen. Then he goes to the other flowers, but perhaps the next one he visits has already exploded and the ripe stigma is exposed in the front of the flower, and as he settles he touches it with his furry body all covered with pollen, and leaves some on it. If you watch the bees doing this yourself, you will find out a number of things which I have not told you, while you may notice how some of the bees are lazy and enter the wrong side of the flower, others are stupid and go to flowers which have already been visited several times, and therefore are of no use, while other bees which come late may open up buds which were not ready for them and steal the honey before the stamens are ripe enough to smother them with pollen. I have watched them opening buds which were still so tightly closed that it took them all their strength to get in. But we must not stop too long with one flower, for almost every flower has some special arrangement of its own, and all are worth study.

Fig. 120. The two kinds of Primrose flowers, A, with long style and stamens low in the petal tube; B, short style, with stamens at the mouth of the petal tube.

The primroses and cowslips are interesting, as they have two kinds of flowers. It you gather a bunch of primroses and look into them you will find that in some you can see the little central green ball of the stigma, and in others at the top of the tube are the five small anthers. These two kinds of flowers make an arrangement which ensures that the pollen from the one kind of flower reaches the stigma of the other. A big fly like the wasp-fly, and several others, visit these flowers most frequently, and carry the pollen from flower A (see fig. 120) to the stigma of B, and the pollen of B to the stigma of A.

Fig. 121. A, Flowerhead of the Daisy; (b) a single little flower from the side with big petals fused together; (c) a single little flower from the middle with very small petals.

As we noticed before, the chief duty of the petals is to act as flags to attract the visiting insects by their bright colours. Now we find that some flowers club together, and grow clustering closely on one head, so that it is sufficient for a few of them to have the flag petals which attract the insect to the group, as it goes from one to the other when once it is there. When a few of the flowers do this, the rest can economise in petals and have quite small ones, and yet all the same they have a good chance of insect visits. Such an arrangement as this is found in the daisy (see fig. 121). A single daisy is not one flower, but a whole bunch of flowers, in which some of the outer flowers of the bunch (see fig. 121 (b)) form big petals, while all the inner ones (fig. 121 (c)) are quite small and inconspicuous, and by themselves would hardly attract any visitors. Just the same thing happens in the cornflower, sunflower, and very many members of the daisy family. The big outer petals attract the insect, and once on the head of flowers it walks about over them, and they all get the benefit.

In such cases we get a division of labour among the flowers of a head, and this represents what is perhaps the highest state of development that flowers have reached.

Fig. 122. Flowerhead of the Cornflower; (a) a single flower from the side with big petals.

PART IV.
THE FIVE GREAT CLASSES OF PLANTS