The science of life : fully illustrated in tone and line and including many diagrams

VEGETABLE LIFE

it and carrying various substances to and fro—water and mineral substances from the mining roots to the light-driven factories in the leaves, finished chemical products from the leaves down to the toiling tissues of the roots. And the roots, sinking hungrily into the soil, sucking up raw materials for the green factories to work upon, branch and branch again into a net of another kind, a net spread not for light, but for moisture. These are the broad essentials of plant anatomy. There are, of course, many other features, many variations on the scheme. There are, for example, parasitic plants, that find it easier to abandon the strenuous light-race and to suck the nourishing juices of their neighbours. The dodder is an example of such a plant, and the mistletoe is an interesting half-way house, battening on the labours of the roots of other plants, for mistletoe perches at the top of a high tree, and its roots, penetrating into the tissue of the latter, suck out the upward stream of moisture and salts for the mistletoe leaves to work upon—an ingeniously effortless way of coming out top in the light-race. And the organs of plants may be turned to other purposes. The leaves may be hard and sharp to repel vegetarian animals, as in gorse, or the twigs may serve the same purpose, as in hawthorn; there may be stores of food, like the swollen roots of carrots, beetroots and turnips or the bulbs, made of fleshy subterranean leaves, of onions and tulips. But these are matters that we shall leave aside here ; the essential thing to remember is that the primary life of a plant is not a food-hunt but a light-hunt, that instead of moving about it grows, that instead of our elaborate apparatus for muscles, nerves and sense-organs it has an elaborate architecture of stems, leaves and roots, and that all these things are simply results of the fact that plants are green.

§ 2 Individuality in Plants

What does it feel like to be a plant ?

In the first place, it is very doubtful whether a plant feels anything at all. In our own bodies sensation depends on the presence of specialized sense-organs and nerves, and there is no trace of either of these structures in a plant. There are philosophers who argue, without too closely defining their terms, that some sort of consciousness must be associated with all matter; that is as may be. In watching the behaviour of plants one gets little evidence

of any sort of conscious sensation. It is, of course, true that many plants grow towards the light, or away from it, or towards moisture, or in a direction opposed to gravitational pull, and in that one discerns a responsiveness to external agencies. But Hammond, an American inventor, once constructed a little machine on wheels that would follow a light as a dog follows its master, and could be led along any desired path in a dark room by simply holding a flashlight in front of it, so that these tropisms, as they are called, do not necessarily imply a considering and deciding mind. The movements that plants perform—such as the turning of flowers and leaves towards the sun, the opening and closing of daisies which depends upon the light, the opening and closing of crocuses or tulips which depends upon temperature, or even the sudden swoon of the sensitive Mimosa pudica when it is touched—are brought about by processes very different from those occurring in our own muscle-fibres. True, there are simple plants, as we shall shortly learn, which skip along by means of lashing tails like animalcules, and Sir J. C. Bose, by using very sensitive apparatus, has detected quivers and shudderings in injured plants ; but we may safely conclude that even if a plant is conscious its mind is something very different, very much more elementary than the highly organized individual consciousness that we ourselves possess. Calves’ foot jelly can be made to quiver, an automobile started on high gear shudders; shuddering by no means implies pain. ;

Looked upon as a cell-community the organization of a flowering plant is somewhere about the level of Obelia in the animal kingdom. Obelia, we noted, is not a discrete, highly specialized individual, but a mass of living tissue, growing and branching and throwing up polyps of various kinds without any very rigid order as occasion demands. Vegetable tissue behaves in much the same way. The structure of a plantbody is by no means as stereotyped as the structure of one of the higher animals ; a primrose does not have a fixed and invariable number of leaves, and the branching of elm-trees is very much more variable than the branching of our own arteries and veins. There is an evident reason for this, for the plant can adapt itself to the particular conditions of illumination under which it finds itself, and grow in such a way as to secure as much light as possible.

Many plants grow and spread by means of creeping underground stems; couch-

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