FOOTNOTES:

Involved in seawrack here we find a race,Which Science, doubting, knows not where to place;On shell or stone is dropped the embryo seed,And quickly vegetates a vital breed.

We cannot wonder that such organisms were long regarded as belonging to the vegetable kingdom. The cups which terminate the branches contain, however, an animal structure, resembling a small Sea Anemone, and possessing arms which capture the food by which the whole colony is nourished. Some of these cups, moreover, differ from the rest, and produce eggs. These then we might be disposed to term ovaries. But in many species they detach themselves from the group and lead an independent existence. Thus we find a complete gradation from structures which, regarded by themselves, we should unquestionably regard as mere organs, to others which are certainly separate and independent beings.

Fig. 2.—Bougainvillea fruticosa; natural size. (After Allman.)Fig. 2.—Bougainvillea fruticosa; natural size. (After Allman.)

Fig. 2 represents, after Allman, a colony of Bougainvillea fruticosa of the natural size. It is a British species, which is found growing on buoys, floating timber, etc., and, says Allman, "When in health and vigour, offers a spectacle unsurpassed in interest by any other species—every branchlet crowned by its graceful hydranth, and budding with Medusæ in all stages of development (Fig. 3), some still in the condition of minute buds, in which no trace of the definite Medusa-form can yet be detected; others, in which the outlines of the Medusa can be distinctly traced within the transparent ectotheque (external layer); others, again, just casting off this thin outer pellicle, and others completely freed from it, struggling with convulsive efforts to break loose from the colony, and finally launchedforth in the full enjoyment of their freedom into the surrounding water. I know of no form in which so many of the characteristic features of a typical hydroid are more finely expressed than in this beautiful species."

Fig. 3.—Bougainvillea fruticosa; magnified to show development.Fig. 3.—Bougainvillea fruticosa; magnified to show development.

Fig. 4 represents the Medusa or free form of this beautiful species.

Fig. 4.—Bougainvillea fruticosa, Medusa-form.Fig. 4.—Bougainvillea fruticosa, Medusa-form.

If we pass to another great group of Zoophytes, that of the Jelly-fishes, we have a very similar case. For our first knowledge of the life-history of these Zoophytes we are indebted to the Norwegian naturalist Sars. Take, for instance, the common Jelly-fish (Medusa aurita) (Fig. 5) of our shores.

The egg is a pear-shaped body (1), covered with fine hairs, by the aid of which it swims about, the broader end in front. After a while it attaches itself, not as might have been expected by the posterior but by the anterior extremity (2). The cilia then disappear, a mouth is formed at the free end, tentacles, first four (3), then eight, and at length as many as thirty (4), are formed, and the little creature resembles in essentials the freshwater polyp (Hydra) of our ponds.

Fig. 5.—Medusa aurita, and progressive stages of development.Fig. 5.—Medusa aurita, and progressive stages of development.

At the same time transverse wrinkles (4) are formed round the body, first near the free extremity and then gradually descending. They become deeper and deeper, and develop lobes or divisions one under the other, as at5. After a while the top ring (and subsequently the others one by one) detaches itself, swims away, and gradually develops into a Medusa (6). Thus, then, the life-history is very similar to that of the Hydroids, only that while in the Hydroids the fixed condition is the more permanent, and the freeswimming more transitory, in the Medusæ, on the contrary, the fixed condition is apparently only a phase in the production of the free swimming animal. In both the one and the other, however, the egg gives rise not to one but to many mature animals. Steenstrup has given to these curious phenomena, many other cases of which occur among the lower animals, and to which he first called attention, the name of alternations of generations.

In the life-history of Infusoria (so called because they swarm in most animal or vegetable infusions) similar difficulties encounter us. The little creatures, many of which are round or oval in form, from time to time become constricted in the middle; the constriction becomes deeper and deeper, and at length the two halves twist themselves apart and swim away. In this case, therefore, there was one, and there are now two exactly similar; but are these two individuals? They are not parent and offspring—that is clear, for they are of the same age; nor are they twins, for there is no parent. As already mentioned, we regard the Caterpillar, Chrysalis,and Butterfly as stages in the life-history of a single individual. But among Zoophytes, and even among some insects, one larva often produces several mature forms. In some species these mature forms remain attached to the larval stock, and we might be disposed to regard the whole as one complex organism. But in others they detach themselves and lead an independent existence.

These considerations then introduce much difficulty into our conception of the idea of an Individual.

But, further than this, we are confronted by by another problem. If we regard a mass of coral as an individual because it arises by continuous growth from a single egg, then it follows that some corals must be thousands of years old.

Some of the lower animals may be cut into pieces, and each piece will develop into anentire organism. In fact the realisation of the idea of an individual gradually becomes more and more difficult, and the continuity of existence, even among the highest animals, gradually forces itself upon us. I believe that as we become more rational, as we realise more fully the conditions of existence, this consideration is likely to have important moral results.

It is generally considered that death is the common lot of all living beings. But is this necessarily so? Infusoria and other unicellular animals multiply by division. That is to say, if we watch one for a certain time, we shall observe, as already mentioned, that a constriction takes place, which grows gradually deeper and deeper, until at last the two halves become quite detached, and each swims away independently. The process is repeated over and over again, and in this manner the species is propagated. Here obviously there is no birth and no death. Such creatures may be killed, but they have no natural term of life. They are, in fact, theoreticallyimmortal. Those which lived millions of years ago may have gone on dividing and subdividing, and in this sense multitudes of the lower animals are millions of years old.

FOOTNOTES:[15]Address to Microscopical Society, 1890.[16]Ants, Bees, and Wasps, andThe Senses of Animals.[17]Prof. Drummond (Tropical Africa) dwells with great force on the manner in which the soil of Central Africa is worked up by the White Ants.[18]Lankester,Comparative Longevity. See also Weismann,Duration of Life.

[15]Address to Microscopical Society, 1890.

[16]Ants, Bees, and Wasps, andThe Senses of Animals.

[17]Prof. Drummond (Tropical Africa) dwells with great force on the manner in which the soil of Central Africa is worked up by the White Ants.

[18]Lankester,Comparative Longevity. See also Weismann,Duration of Life.

Flower in the crannied wall,I pluck you out of the crannies,I hold you here, root and all, in my hand,Little flower—butifI could understandWhat you are, root and all, and all in all,I should know what God and man is.Tennyson.

Tennyson.

We are told that in old days the Fairies used to give presents of Flowers and Leaves to those whom they wished to reward, or whom they loved best; and though these gifts were, it appears, often received with disappointment, still it will probably be admitted that flowers have contributed more to the happiness of our lives than either gold or silver or precious stones; and that our happiest days have been spent out-of-doors in the woods and fields, when we have

... found in every woodland wayThe sunlight tint of Fairy Gold.[19]

To many minds Flowers acquired an additional interest when it was shown thatthere was a reason for their colour, size, and form—in fact, for every detail of their organisation. If we did but know all that the smallest flower could tell us, we should have solved some of the greatest mysteries of Nature. But we cannot hope to succeed—even if we had the genius of Plato or Aristotle—without careful, patient, and reverent study. From such an inquiry we may hope much; already we have glimpses, enough to convince us that the whole history will open out to us conceptions of the Universe wider and grander than any which the Imagination alone would ever have suggested.

Attempts to explain the forms, colours, and other characteristics of animals and plants are by no means new. Our Teutonic forefathers had a pretty story which explained certain points about several common plants. Balder, the God of Mirth and Merriment, was, characteristically enough, regarded as deficient in the possession of immortality. The other divinities, fearing to lose him, petitioned Thor to make him immortal, and the prayer was granted on condition that every animal andplant would swear not to injure him. To secure this object, Nanna, Balder's wife, descended upon the earth. Loki, the God of Envy, followed her, disguised as a crow (which at that time were white), and settled on a little blue flower, hoping to cover it up, so that Nanna might overlook it. The flower, however, cried out "forget-me-not, forget-me-not," and has ever since been known under that name. Loki then flew up into an oak and sat on a mistletoe. Here he was more successful. Nanna carried off the oath of the oak, but overlooked the mistletoe. She thought, however, and the divinities thought, that she had successfully accomplished her mission, and that Balder had received the gift of immortality.

One day, supposing Balder proof, they amused themselves by shooting at him, posting him against a Holly. Loki tipped an arrow with a piece of Mistletoe, against which Balder was not proof, and gave it to Balder's brother. This, unfortunately, pierced him to the heart, and he fell dead. Some drops of his blood spurted on to the Holly, whichaccounts for the redness of the berries; the Mistletoe was so grieved that she has ever since borne fruit like tears; and the crow, whose form Loki had taken, and which till then had been white, was turned black.

This pretty myth accounts for several things, but is open to fatal objections.

Recent attempts to explain the facts of Nature are not less fascinating, and, I think, more successful.

Why then this marvellous variety? this inexhaustible treasury of beautiful forms? Does it result from some innate tendency in each species? Is it intentionally designed to delight the eye of man? Or has the form and size and texture some reference to the structure and organisation, the habits and requirements of the whole plant?

I shall never forget hearing Darwin's paper on the structure of the Cowslip and Primrose, after which even Sir Joseph Hooker compared himself to Peter Bell, to whom

A primrose by a river's brimA yellow primrose was to him,And it was nothing more.

We all, I think, shared the same feeling, and found that the explanation of the flower then given, and to which I shall refer again, invested it with fresh interest and even with new beauty.

A regular flower, such, for instance, as a Geranium or a Pink, consists of four or more whorls of leaves, more or less modified: the lowest whorl is the Calyx, and the separate leaves of which it is composed, which however are sometimes united into a tube, are called sepals; (2) a second whorl, the corolla, consisting of coloured leaves called petals, which, however, like those of the Calyx, are often united into a tube; (3) of one or more stamens, consisting of a stalk or filament, and a head or anther, in which the pollen is produced; and (4) a pistil, which is situated in the centre of the flower, and at the base of which is the Ovary, containing one or more seeds.

Almost all large flowers are brightly coloured, many produce honey, and many are sweet-scented.

What, then, is the use and purpose of this complex organisation?

It is, I think, well established that the main object of the colour, scent, and honey of flowers is to attract insects, which are of use to the plant in carrying the pollen from flower to flower.

In many species the pollen is, and no doubt it originally was in all, carried by the air. In these cases the chance against any given grain of pollen reaching the pistil of another flower of the same species is of course very great, and the quantity of pollen required is therefore immense.

In species where the pollen is wind-borne as in most of our trees—firs, oaks, beech, ash, elm, etc., and many herbaceous plants, the flowers are as a rule small and inconspicuous, greenish, and without either scent or honey. Moreover, they generally flower early, so that the pollen may not be intercepted by the leaves, but may have a better chance of reaching another flower. And they produce an immense quantity of pollen, as otherwise there would be little chance that any would reach the female flower. Every one must have noticed the clouds of pollen produced bythe Scotch Fir. When, on the contrary, the pollen is carried by insects, the quantity necessary is greatly reduced. Still it has been calculated that a Peony flower produces between 3,000,000 and 4,000,000 pollen grains; in the Dandelion, which is more specialised, the number is reduced to about 250,000; while in such a flower as the Dead-nettle it is still smaller.

The honey attracts the insects; while the scent and colour help them to find the flowers, the scent being especially useful at night, which is perhaps the reason why evening flowers are so sweet.

It is to insects, then, that flowers owe their beauty, scent, and sweetness. Just as gardeners, by continual selection, have added so much to the beauty of our gardens, so to the unconscious action of insects is due the beauty, scent, and sweetness of the flowers of our woods and fields.

Let us now apply these views to a few common flowers. Take, for instance, the White Dead-nettle.

The corolla of this beautiful and familiarflower (Fig. 6) consists of a narrow tube, somewhat expanded at the upper end (Fig. 7), where the lower lobe forms a platform, on each side of which is a small projecting tooth (Fig. 8,m). The upper portion of the corolla is an arched hood (co), under which lie four anthers (a a), in pairs, while between them, and projecting somewhat downwards, is the pointed pistil (st); the tube at the lower part contains honey, and above the honey is a row of hairs running round the tube.

Fig. 6—White Dead-nettle.Fig. 6—White Dead-nettle.

Now, why has the flower this peculiar form? What regulates the length of the tube? What is the use of the arch? What lesson do the little teeth teach us? What advantage is the honey to the flower? Of what use is the fringe of hairs? Why does the stigma project beyond theanthers? Why is the corolla white, while the rest of the plant is green?

Fig. 7.Fig. 7.

Fig. 8.Fig. 8.

The honey of course serves to attract the Humble Bees by which the flower is fertilised, and to which it is especially adapted; the white colour makes the flower more conspicuous; the lower lip forms the stage on which the Bees may alight; the length of the tube is adapted to that of their proboscis; its narrowness and the fringe of fine hairs exclude small insects which might rob the flower of its honey without performing any service in return; the arched upper lip protects the stamens and pistil, and prevents rain-drops from choking up the tube and washing away the honey; the little teeth are, I believe, ofno use to the flower in its present condition, they are the last relics of lobes once much larger, and still remaining so in some allied species, but which in the Dead-nettle, being no longer of any use, are gradually disappearing; the height of the arch has reference to the size of the Bee, being just so much above the alighting stage that the Bee, while sucking the honey, rubs its back against the hood and thus comes in contact first with the stigma and then with the anthers, the pollen-grains from which adhere to the hairs on the Bee's back, and are thus carried off to the next flower which the Bee visits, when some of them are then licked off by the viscid tip of the stigma.[20]

Fig. 9.Fig. 9.

Fig. 10.Fig. 10. Fig. 11.

In the Salvias, the common blue Salvia of our gardens, for instance,—a plant allied to the Dead-nettle,—the flower (Fig. 9) is constructed on the same plan, but the arch is much larger, so that the back of the Bee does not nearly reach it. The stamens, however, have undergone a remarkable modification. Two of them have become small and functionless. In the other two the anthers or cells producing the pollen, which in most flowers form together a round knob or head at the top of the stamen, are separated by a long arm, which plays on the top of the stamen as on a hinge. Of these two arms one hangs down into the tube, closing the passage, while the other lies under the arched upper lip. When the Bee pushes its proboscis down the tube (Fig. 11) it presses the lower arm to one side, and the upper arm consequently descends, tapping theBee on the back, and dusting it with pollen. When the flower is a little older the pistil (Fig. 9,p) has elongated so that the stigma (Fig. 10,st) touches the back of the Bee and carries off some of the pollen. This sounds a little complicated, but is clear enough if we take a twig or stalk of grass and push it down the tube, when one arm of each of the two larger stamens will at once make its appearance. It is one of the most beautiful pieces of plant mechanism which I know, and was first described by Sprengel, a poor German schoolmaster.

At first sight it may seem an objection to the view here advocated that the flowers in some species—as, for instance, the common Snapdragon (Antirrhinum), which, according to the above given tests, ought to be fertilised by insects—are entirely closed. A little consideration, however, will suggest the reply. The Snapdragon is especially adapted forfertilisation by Humble Bees. The stamens and pistil are so arranged that smaller species would not effect the object. It is therefore an advantage that they should be excluded, and in fact they are not strong enough to move the spring. The Antirrhinum is, so to speak, a closed box, of which the Humble Bees alone possess the key.

Other flowers such as the Furze, Broom, Laburnum, etc., are also opened by Bees. The petals lock more or less into one another, and the flower remains at first closed. When, however, the insect alighting on it presses down the keel, the flower bursts open, and dusts it with pollen.

In the above cases the flower once opened does not close again. In others, such as the Sweet Pea and the Bird's-foot Lotus, Naturehas been more careful. When the Bee alights it clasps the "wings" of the flower with its legs, thus pressing them down; they are, however, locked into the "keel," or lower petal, which accordingly is also forced down, thus exposing the pollen which rubs against, and part of which sticks to, the breast of the Bee. When she leaves the flower the keel and wings rise again, thus protecting the rest of the pollen and keeping it ready until another visitor comes. It is easy to carry out the same process with the fingers.

Fig. 12. Fig. 13.Fig. 12. Fig. 13.Flower and Pollen of Primrose

In the Primrose and Cowslip, again, we find quite a different plan. It had long been known that if a number of Cowslips or Primroses are examined, about half would be found to have the stigma at the top of the tube and the stamens half way down, while in the other half the stamens are at the top and the stigma half way down. These two forms are about equally numerous, but never occur on the same stock. They have been long known to children and gardeners, who call them thrum-eyed and pin-eyed. Mr. Darwin was the first to explain the significance of this curious difference. It cost him several years of patient labour, but when once pointed out it is sufficiently obvious. An insect thrusting its proboscis down a primrose of the long-styled form (Fig. 12) would dust its proboscis at a part (a) which, when it visited a short-styled flower (Fig. 13), would come just opposite the head of the pistil (st), and could not fail to deposit some of the pollen on the stigma. Conversely, an insect visiting a short-styled plant would dust its proboscis at a part fartherfrom the tip; which, when the insect subsequently visited a long-styled flower, would again come just opposite to the head of the pistil. Hence we see that by this beautiful arrangement insects must carry the pollen of the long-styled form to the short-styled, andvice versâ.

The economy of pollen is not the only advantage which plants derive from these visits of Insects. A second and scarcely less important is that they tend to secure "cross fertilisation"; that is to say, that the seed shall be fertilised by pollen from another plant. The fact that "cross fertilisation" is of advantage to the plant doubtless also explains the curious arrangement that in many plants the stamen and pistil do not mature at the same time—the former having shed their pollen before the pistil is mature; or, which happens less often, the pistil having withered before the pollen is ripe. In most Geraniums, Pinks, etc., for instance, and many allied species, the stamens ripen first, and are followed after an interval by the pistil.

The Nottingham Catchfly (Silene nutans) is a very interesting case. The flower is adapted to be fertilised by Moths. Accordingly it opens towards evening, and as is generally the case with such flowers, is pale in colour, and sweet-scented. There are two sets of stamens, five in each set. The first evening that the flower opens one set of stamens ripen and expose their pollen. Towards morning these wither away, the flower shrivels up, ceases to emit scent, and looks as if it were faded. So it remains all next day. Towards evening it reopens, the second set of stamens have their turn, and the flower again becomes fragrant. By morning, however, the second set of stamens have shrivelled, and the flower is again asleep. Finally on the third evening it reopens for the last time, the long spiral stigmas expand, and can hardly fail to be fertilised with the pollen brought by Moths from other flowers.

In the hanging flowers of Heaths the stamens form a ring, and each one bears two horns. When the Bee inserts its proboscis into the flower to reach the honey, it is sure to press against one of these horns, the ring is dislocated, and the pollen falls on to the head of the insect. In fact, any number of other interesting cases might be mentioned.

Bees are intelligent insects, and would soon cease to visit flowers which did not supply them with food. Flies, however, are more stupid, and are often deceived. Thus in our lovely little Parnassia, five of the ten stamens have ceased to produce pollen, but are prolonged into fingers, each terminating in a shining yellow knob, which looks exactly like a drop of honey, and by which Flies are continuallydeceived. Paris quadrifolia also takes them in with a deceptive promise of the same kind. Some foreign plants have livid yellow and reddish flowers, with a most offensive smell, and are constantly visited by Flies, which apparently take them for pieces of decaying meat.

Fig. 14.—Arum.Fig. 14.—Arum.

The flower of the common Lords and Ladies (Arum) of our hedges is a very interesting case. The narrow neck bears a number of hairs pointing downwards. The stamens are situated above the stigma, which comes to maturity first. Small Flies enter the flower apparently for shelter, but the hairs prevent them from returning, and they are kept captive until the anthers have shed their pollen. Then, when the Flies have been well dusted, the hairs shrivel up, leaving a clear road, and the prisoners are permitted to escape. The tubular flowers of Aristolochia offer a very similar case.

If the views here advocated are correct, it follows that the original flowers were small and green, as wind-fertilised flowers are even now. But such flowers are inconspicuous. Those which are coloured, say yellow or white, are of course much more visible and more likely to be visited by insects. I have elsewhere given my reasons for thinking that under these circumstances some flowers became yellow, that some of them became white, others subsequently red, and some finally blue. It will be observed that red and blue flowers are as a rule highly specialised, such as Aconites and Larkspurs as compared with Buttercups; blue Gentians as compared with yellow, etc. I have found by experiment that Bees are especially partial to blue and pink.

Tubular flowers almost always, if not always, contain honey, and are specially suited to Butterflies and Moths, Bees and Flies. Those which are fertilised by Moths generallycome out in the evening, are often very sweetly scented, and are generally white or pale yellow, these colours being most visible in the twilight.

Aristotle long ago noticed the curious fact that in each journey Bees confine themselves to some particular flower. This is an economy of labour to the Bee, because she has not to vary her course of proceeding. It is also an advantage to the plants, because the pollen is carried from each flower to another of the same species, and is therefore less likely to be wasted.

After the flower comes the seed, often contained in a fruit, and which itself encloses the future plant. Fruits and seeds are adapted for dispersion, beautifully and in various ways: some by the wind, being either provided with a wing, as in the fruits of many trees—Sycamores, Ash, Elms, etc.; or with a hairy crown or covering, as with Thistles, Dandelions, Willows, Cotton plant, etc.

Some seeds are carried by animals; either as food—such as most edible fruits and seeds, acorns, nuts, apples, strawberries, raspberries, blackberries, plums, grasses, etc.—or involuntarily, the seeds having hooked hairs or processes, such as burrs, cleavers, etc.

Some seeds are scattered by the plants themselves, as, for instance, those of many Geraniums, Violets, Balsams, Shamrocks, etc. Our little Herb Robert throws its seeds some 25 feet.

Some seeds force themselves into the ground, as those of certain grasses, Cranes'-bills (Erodiums), etc.

Some are buried by the parent plants, as those of certain clovers, vetches, violets, etc.

Some attach themselves to the soil, as those of the Flax; or to trees, as in the case of the Mistletoe.

Again, as regards the leaves there can, I think, be no doubt that similar considerationsof utility are applicable. Their forms are almost infinitely varied. To quote Ruskin's vivid words, they "take all kinds of strange shapes, as if to invite us to examine them. Star-shaped, heart-shaped, spear-shaped, arrow-shaped, fretted, fringed, cleft, furrowed, serrated, sinuated, in whorls, in tufts, in spires, in wreaths, endlessly expressive, deceptive, fantastic, never the same from foot-stalk to blossom, they seem perpetually to tempt our watchfulness and take delight in outstepping our wonder."

But besides these differences of mere form, there are many others: of structure, texture, and surface; some are scented or have a strong taste, or acrid juice, some are smooth, others hairy; and the hairs again are of various kinds.

I have elsewhere[21]endeavoured to explain some of the causes which have determined these endless varieties. In the Beech, for instance (Fig. 15), the leaf has an area of about 3 square inches. The distance between the buds is about 1-1/4 inch, and the leaves lie inthe general plane of the branch, which bends slightly at each internode. The basal half of the leaf fits the swell of the twig, while the upper half follows the edge of the leaf above; and the form of the inner edge being thus determined, decides that of the outer one also.

Fig. 15.—Beech.Fig. 15.—Beech.

The weight, and consequently the size of the leaf, is limited by the strength of the twig; and, again, in a climate such as ours it is important to plants to have their leaves so arranged as to secure the maximum of light. Hence in leaves which lie parallel to the plane of the boughs, as in the Beech, the width depends partly on the distance between the buds; if the leaves were broader, they would overlap, if they were narrower, space would be wasted. Consequently the width being determined by the distance between the buds, and the size depending on the weightwhich the twig can safely support, the length also is determined. This argument is well illustrated by comparing the leaves of the Beech with those of the Spanish Chestnut. The arrangement is similar, and the distance between the buds being about the same, so is the width of the leaves. But the terminal branches of the Spanish Chestnut being much stronger, the leaves can safely be heavier; hence the width being fixed, they grow in length and assume the well-known and peculiar sword-blade shape.

In the Sycamores, Maples (Fig. 16), and Horse-Chestnuts the arrangement is altogether different. The shoots are stiff and upright with leaves placed at right angles to the branches instead of being parallel to them. The leaves are in pairs and decussate with one another; while the lower ones have long petioles which bring them almost to the level of the upper pairs, the whole thus forming a beautiful dome.

For leaves arranged as in the Beech the gentle swell at the base is admirably suited; but in a crown of leaves such as those of theSycamore, space would be wasted, and it is better that they should expand at once, so soon as their stalks have carried them free from the upper and inner leaves.

Fig. 16.—Acer platanoides.Fig. 16.—Acer platanoides.

In the Black Poplar the arrangement of the leaves is again quite different. The leaf stalk is flattened, so that the leaves hang vertically. In connection with this it will be observed that while in most leaves the upper and under surfaces are quite unlike, in the Black Poplar on the contrary they are very similar. The stomata or breathing holes, moreover, which in the leaves of most trees are confined to the under surface, are in this species nearly equally numerous on both.

The "Compass" Plant of the American prairies, a plant not unlike a small sunflower, is another species with upright leaves, which growing in the wide open prairies tend to point north and south, thus exposing both surfaces equally to the light and heat. Such a position also affects the internal structure of the leaf, the two sides becoming similar in structure, while in other cases the upper and under surfaces are very different.

In the Yew the leaves are inserted close to one another, and are linear; while in the Box they are further apart and broader. In other cases the width of the leaves is determined by what botanists call the "Phyllotaxy." Some plants have the leaves opposite, each pair being at right angles with the pairs above and below.

In others they are alternate, and arranged round the stem in a spiral. In one very common arrangement the sixth leaf stands directly over the first, the intermediate ones forming a spiral which has passed twice round the stem. This, therefore, is known as the 2/5 arrangement. Common cases are 1/2, 1/3, 2/5, 3/8,and 5/13. In the first the leaves are generally broad, in the 3/8 arrangement they are elliptic, in the 5/13 and more complicated arrangements nearly linear. The Willows afford a very interesting series. Salix herbacea has the 1/3 arrangement and rounded leaves, Salix caprea elliptic leaves and 2/5, Salix pentandra lancet-shaped leaves and 3/8, and S. incana linear leaves and a 5/13 arrangement. The result is that whether the series consists of 2, 3, 5, 8, or 13 leaves, in every case, if we look perpendicularly at a twig the leaves occupy the whole circle.

In herbaceous plants upright leaves as a rule are narrow, which is obviously an advantage, while prostrate ones are broad.

AQUATIC VEGETATION, BRAZIL. To face page 145.AQUATIC VEGETATION, BRAZIL.To face page 145.

Many aquatic plants have two kinds of leaves; some more or less rounded, which float on the surface; and others cut up into narrow segments, which remain below. The latter thus present a greater extent of surface. In air such leaves would be unable even to support their own weight, much less to resist the force of the wind. In still air, however, for the same reason, finely-divided leaves may be an advantage, while in exposed positions compact and entire leaves are more suitable. Hence herbaceous plants tend to have divided, bushes and trees entire, leaves. There are many cases when even in the same family low and herb-like species have finely-cut leaves, while in shrubby or ligneous ones they more or less resemble those of the Laurel or Beech.

These considerations affect trees more than herbs, because trees stand more alone, while herbaceous plants are more affected by surrounding plants. Upright leaves tend to be narrow, as in the case of grasses; horizontal leaves, on the contrary, wider. Large leaves are more or less broken up into leaflets, as in the Ash, Mountain-Ash, Horse-Chestnut, etc.

The forms of leaves depend also much on the manner in which they are packed into the buds.

The leaves of our English trees, as I have already said, are so arranged as to secure the maximum of light; in very hot countries the reverse is the case. Hence, in Australia, for instance, the leaves are arranged not horizontally, but vertically, so as to present, not their surfaces, but their edges, to the sun. One English plant, a species of lettuce, has the same habit. This consideration has led also to other changes. In many species the leaves are arranged directly under, so as to shelter, one another. The Australian species of Acacia have lost their true leaves, and the parts which in them we generally call leaves are in reality vertically-flattened leaf stalks.

In other cases the stem itself is green, and to some extent replaces the leaves. In our common Broom we see an approach to this, and the same feature is more marked in Cactus. Or the leaves become fleshy, thus offering, in proportion to their volume, a smaller surface for evaporation. Of this the Stonecrops, Mesembryanthemum, etc., are familiar instances. Other modes of checkingtranspiration and thus adapting plants to dry situations are by the development of hairs, by the formation of chalky excretions, by the sap becoming saline or viscid, by the leaf becoming more or less rolled up, or protected by a covering of varnish.

Our English trees are for the most part deciduous. Leaves would be comparatively useless in winter when growth is stopped by the cold; moreover, they would hold the snow, and thus cause the boughs to be broken down. Hence perhaps the glossiness of Evergreen leaves, as, for instance, of the Holly, from which the snow slips off. In warmer climates trees tend to retain their leaves, and some species which are deciduous in the north become evergreen, or nearly so, in the south of Europe. Evergreen leaves are as a rule tougher and thicker than those which drop off in autumn; they require more protection from the weather. But some evergreen leaves are much longer lived than others; those of the Evergreen Oak do not survive a second year, those of the Scotch Pine live for three, of the Spruce Fir, Yew, etc., for eight or ten, of thePinsapo even eighteen. As a general rule the Conifers with short leaves keep them on for several years, those with long ones for fewer, the length of the leaf being somewhat in the inverse ratio to the length of its life; but this is not an invariable criterion, as other circumstances also have to be taken into consideration.

Leaves with strong scent, aromatic taste, or acrid juice, are characteristic of dry regions, where they run especial danger of being eaten, and where they are thus more or less effectively protected.

The hairs of plants are useful in various ways. In some cases (1) they keep off superfluous moisture; in others (2) they prevent too rapid evaporation; in some (3) they serve as a protection against too glaring light; in some (4) they protect the plant from browsing quadrupeds; in others (5) from being eaten by insects; or, (6) serve as a quickset hedge to prevent access to the flowers.

In illustration of the first case I may refer to many alpine plants, the well-known Edelweiss, for instance, where the woolly covering of hairs prevents the "stomata," or minute pores leading into the interior of the leaf, from being clogged up by rain, dew, or fog, and thus enable them to fulfil their functions as soon as the sun comes out.

As regards the second case many desert and steppe-plants are covered with felty hairs, which serve to prevent too rapid evaporation and consequent loss of moisture.

The woolly hairy leaves of the Mulleins (Verbascum) doubtless tend to protect them from being eaten, as also do the spines of Thistles, and those of Hollies, which, be it remarked, gradually disappear on the upper leaves which browsing quadrupeds cannot reach.

I have already alluded to the various ways in which flowers are adapted to fertilisation by insects. But Ants and other small creeping insects cannot effectually secure this object. Hence it is important that they should be excluded, and not allowed to carry off the honey,for which they would perform no service in return. In many cases, therefore, the opening of the flower is either contracted to a narrow passage, or is itself protected by a fringe of hairs. In others the peduncle, or the stalk of the plant, is protected by a hedge, or chevaux de frise, of hairs.

In this connection I might allude to the many plants which are more or less viscid. This also is in most cases a provision to preclude creeping insects from access to the flowers.

There are various other kinds of hairs to which I might refer—glandular hairs, secretive hairs, absorbing hairs, etc. It is marvellous how beautifully the form and structure of leaves is adapted to the habits and requirements of the plants, but I must not enlarge further on this interesting subject.

The time indeed will no doubt come when we shall be able to explain every difference of form and structure, almost infinite as these differences are.

The character of the vegetation is of course greatly influenced by that of the soil. In this respect granitic and calcareous regions offer perhaps the best marked contrast.

There are in Switzerland two kinds of Rhododendrons, very similar in their flowers, but contrasted in their leaves: Rhododendron hirsutum having them hairy at the edges as the name indicates; while in R. ferrugineum they are rolled, but not hairy, at the edges, and become ferrugineous on the lower side. This species occurs in the granitic regions, where R. hirsutum does not grow.

The Yarrows (Achillea) afford us a similar case. Achillea atrata and A. moschata will live either on calcareous or granitic soil, but in a district where both occur, A. atrata grows so much the more vigorously of the two if the soil is calcareous that it soon exterminates A. moschata; while in granite districts, on the contrary, A. moschata is victorious and A. atrata disappears.

Every keen sportsman will admit that a varied "bag" has a special charm, and the botanist in a summer's walk may see at least a hundred plants in flower, all with either the interest of novelty, or the charm of an old friend.

In many cases the Seedlings afford us an interesting insight into the former condition of the plant. Thus the leaves of the Furze are reduced to thorns; but those of the Seedling are herbaceous and trifoliate like those of the Herb Genet and other allied species, subsequent ones gradually passing into spines. This is evidence that the ancestors of the Furze bore leaves.

Plants may be said to have their habits as well as animals.

Many flowers close their petals during rain; the advantage of which is that it prevents the honey and pollen from being spoiltor washed away. Everybody, however, has observed that even in fine weather certain flowers close at particular hours. This habit of going to sleep is surely very curious. Why should flowers do so? In animals we can better understand it; they are tired and require rest. But why should flowers sleep? Why should some flowers do so, and not others? Moreover, different flowers keep different hours. The Daisy opens at sunrise and closes at sunset, whence its name "day's-eye." The Dandelion (Leontodon) is said to open about seven and to close about five; Arenaria rubra to be open from nine to three; the White Water Lily (Nymphæa), from about seven to four; the common Mouse-ear Hawk-weed (Hieracium) from eight to three; the Scarlet Pimpernel (Anagallis) to waken at seven and close soon after two; Tragopogon pratensis to open at four in the morning, and close just before twelve, whence its English name, "John go to bed at noon." Farmers' boys in some parts are said to regulate their dinner time by it. Other flowers, on the contrary, open in the evening.

Now it is obvious that flowers which are fertilised by night-flying insects would derive no advantage from being open by day; and on the other hand, that those which are fertilised by bees would gain nothing by being open at night. Nay it would be a distinct disadvantage, because it would render them liable to be robbed of their honey and pollen, by insects which are not capable of fertilising them. I have ventured to suggest then that the closing of flowers may have reference to the habits of insects, and it may be observed also in support of this, that wind-fertilised flowers do not sleep; and that many of those flowers which attract insects by smell, open and emit their scent at particular hours; thus Hesperis matronalis and Lychnis vespertina smell in the evening, and Orchis bifolia is particularly sweet at night.

But it is not the flowers only which "sleep" at night; in many species the leaves also change their position, and Darwin has given strong reasons for considering that the object is to check transpiration and thus tend to a protection against cold.

The behaviour of plants with reference to rain affords many points of much interest. The Germander Speedwell (Veronica) has two strong rows of hairs, the Chickweed (Stellaria) one, running down the stem and thus conducting the rain to the roots. Plants with a main tap-root, like the Radish or the Beet, have leaves sloping inwards so as to conduct the rain towards the axis of the plant, and consequently to the roots; while, on the contrary, where the roots are spreading the leaves slope outwards.

In other cases the leaves hold the rain or dew drops. Every one who has been in the Alps must have noticed how the leaves of the Lady's Mantle (Alchemilla) form little cups containing each a sparkling drop of icy water. Kerner has suggested that owing to these cold drops, the cattle and sheep avoid the leaves.

In many cases plants mimic others which are better protected than themselves. Thus Matricaria Chamomilla mimics the true Chamomile, which from its bitterness is not eaten by quadrupeds. Ajuga Chamæpitys mimics Euphorbia Cyparissias, with which it often grows, and which is protected by its acrid juice. The most familiar case, however, is that of the Stinging and the Dead Nettles. They very generally grow together, and though belonging to quite different families are so similar that they are constantly mistaken for one another. Some Orchids have a curious resemblance to insects, after which they have accordingly been named the Bee Orchis, Fly Orchis, Butterfly Orchis, etc., but it has not yet been satisfactorily shown what advantage the resemblance is to the plant.

The transference of pollen from plant toplant is by no means the only service which insects render.

Ants, for instance, are in many cases very useful to plants. They destroy immense numbers of caterpillars and other insects. Forel observing a large Ants' nest counted more than 28 insects brought in as food per minute. In some cases Ants attach themselves to particular trees, constituting a sort of bodyguard. A species of Acacia, described by Belt, bears hollow thorns, while each leaflet produces honey in a crater-formed gland at the base, as well as a small, sweet, pear-shaped body at the tip. In consequence it is inhabited by myriads of a small ant, which nests in the hollow thorns, and thus finds meat, drink, and lodging all provided for it. These ants are continually roaming over the plant, and constitute a most efficient bodyguard, not only driving off the leaf-eating ants, but, in Belt's opinion, rendering the leaves less liable to be eaten by herbivorous mammalia. Delpino mentions that on one occasion he was gathering a flower of Clerodendrum, when he was himself suddenly attacked by a whole army of small ants.

In the cases above mentioned the relation between flowers and insects is one of mutual advantage. But this is by no means an invariable rule. Many insects, as we all know, live on plants, but it came upon botanists as a surprise when our countryman Ellis first discovered that some plants catch and devour insects. This he observed in a North American plant, Dionsea, the leaves of which are formed something like a rat-trap, with a hinge in the middle, and a formidable row of spines round the edge. On the surface are a few very sensitive hairs, and the moment any small insect alights on the leaf and touches one of these hairs the two halves of the leaf close up quickly and catch it. The surface then throws out a glutinous secretion, by means of which the leaf sucks up the nourishment contained in the insect.

Our common Sun-dews (Drosera) arealso insectivorous, the prey being in their case captured by glutinous hairs. Again, the Bladderwort (Utricularia), a plant with pretty yellow flowers, growing in pools and slow streams, is so called because it bears a great number of bladders or utricles, each of which is a real miniature eel-trap, having an orifice guarded by a flap opening inwards which allows small water animals to enter, but prevents them from coming out again. The Butterwort (Pinguicula) is another of these carnivorous plants.

While considering Plant life we must by no means confine our attention to the higher orders, but must remember also those lower groups which converge towards the lower forms of animals, so that in the present state of our knowledge the two cannot always be distinguished with certainty. Many of them differ indeed greatly from the ordinary conception of a plant. Even the comparatively highly organised Sea-weeds multiply by meansof bodies called spores, which an untrained observer would certainly suppose to be animals. They are covered by vibratile hairs or "cilia," by means of which they swim about freely in the water, and even possess a red spot which, as being especially sensitive to light, may be regarded as an elementary eye, and with the aid of which they select some suitable spot, to which they ultimately attach themselves.

It was long considered as almost a characteristic of plants that they possessed no power of movement. This is now known to be an error. In fact, as Darwin has shown, every growing part of a plant is in continual and even constant rotation. The stems of climbing plants make great sweeps, and in other cases, when the motion is not so apparent, it nevertheless really exists. I have already mentioned that many plants change the position of their leaves or flowers, or, as it is called, sleep at night.

The common Dandelion raises its head when the florets open, opens and shuts morning and evening, then lies down again while the seeds are ripening, and raises itself asecond time when they are ready to be carried away by the wind.

Valisneria spiralis is a very interesting case. It is a native of European rivers, and the female flower has a long spiral stalk which enables it to float on the surface of the water. The male flowers have no stalks, and grow low down on the plant. They soon, however, detach themselves altogether, rise to the surface, and thus are enabled to fertilise the female flowers among which they float. The spiral stalk of the female flower then contracts and draws it down to the bottom of the water so that the seeds may ripen in safety. Many plants throw or bury their seeds.

The sensitive plants close their leaves when touched, and the leaflets of Desmodium gyrans are continually revolving. I have already mentioned that the spores of sea-weeds swim freely in the water by means of cilia. Some microscopic plants do so throughout a great part of their lives.

A still lower group, the Myxomycetes, which resemble small, more or less branched, masses of jelly, and live in damp soil, amongdecaying leaves, under bark and in similar moist situations, are still more remarkably animal like. They are never fixed, but in almost continual movement, due to differences of moisture, warmth, light, or chemical action. If, for instance, a moist body is brought into contact with one of their projections, or "pseudopods," the protoplasm seems to roll itself in that direction, and so the whole organism gradually changes its place. So again, while a solution of salt, carbonate of potash, or saltpetre causes them to withdraw from the danger, an infusion of sugar, or tan, produces a flow of protoplasm towards the source of nourishment. In fact, in the same way it rolls over and round its food, absorbing what is nutritious as it passes along. In cold weather they descend into the soil, and one of them (Œthalium), which lives in tan pits, descends in winter to a depth of several feet. When about to fructify it changes its habits, seeks the light instead of avoiding it, climbs upwards, and produces its fruit above ground.

The total number of living species of plants may be roughly estimated at 500,000, and there is not one, of which we can say that the structure, uses, and life-history are yet fully known to us. Our museums contain large numbers which botanists have not yet had time to describe and name. Even in our own country not a year passes without some additional plant being discovered; as regards the less known regions of the earth not half the species have yet been collected. Among the Lichens and Fungi especially many problems of their life-history, some, indeed, of especial importance to man, still await solution.

Our knowledge of the fossil forms, moreover, falls far short even of that of existing species, which, on the other hand, they must have greatly exceeded in number. Every difference of form, structure, and colour has doubtless some cause and explanation, so that the field for research is really inexhaustible.

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