The Beauties of Nature, and the Wonders of the World We Live In Part 8

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.

ON SEEDLINGS

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 pa.s.sing 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.

SLEEP OF PLANTS

Many flowers close their petals during rain; the advantage of which is that it prevents the honey and pollen from being spoilt or 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 (Nymphaea), 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.

BEHAVIOUR OF LEAVES IN RAIN

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.

MIMICRY

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 Chamaepitys 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, b.u.t.terfly Orchis, etc., but it has not yet been satisfactorily shown what advantage the resemblance is to the plant.

ANTS AND PLANTS

The transference of pollen from plant to plant 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, const.i.tuting 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 const.i.tute 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.

INSECTIVOROUS PLANTS

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) are also 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 b.u.t.terwort (Pinguicula) is another of these carnivorous plants.

MOVEMENTS OF 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 means of 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 a second 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, ma.s.ses of jelly, and live in damp soil, among decaying 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 pa.s.ses along. In cold weather they descend into the soil, and one of them (Oethalium), 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.

IMPERFECTION OF OUR KNOWLEDGE

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 pa.s.ses 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.

FOOTNOTES:

[19] Thomson.

[20] Lubbock, _Flowers and Insects_.

[21] _Flowers, Fruits, and Leaves._

CHAPTER V

WOODS AND FIELDS

"By day or by night, summer or winter, beneath trees the heart feels nearer to that depth of life which the far sky means. The rest of spirit, found only in beauty, ideal and pure, comes there because the distance seems within touch of thought."

JEFFERIES.

CHAPTER V