The structure of plants contributes essentially both to their own preservation, and that of others. But the wisdom of the Creator appears very remarkable in the manner of the growth of trees. For as their roots descend deeper than those of other plants, provision is thereby made that they shall not rob them too much of nourishment;[99] and what is still more, a stem, not above a span in diameter, often shoots its branches very high; these bear perhaps many thousand buds, each of which is a plant, with its leaves, flowers, and stipulæ. Now if all these grew on the plain, they would take up a thousand times as much space as trees do; and, in this case, there would scarcely be room in all the earth for so many plants as at present trees alone afford. Besides, plants that shoot up in this way are more easily preserved from cattle by a natural defence: their leaves also, falling in autumn, cover the plants growing about them against the rigor of the winter; and, in the summer, they afford a pleasing shade, not only to animals, but to plants, against the intense heat of the sun. We may add, that trees, like all other vegetables, imbibe water from the earth: which does not circulate again to the root, but being dispersed like small rain, by the transpiration of the leaves, moistens the plants that grow around. Many plants and shrubs are armed with thorns, as the buckthorn, sloe, carduus, cotton-thistle, &c: these serve to keep off animals, which otherwise would destroy their fruit. At the same time, they cover many other plants, especially of the annual kind, under their branches. Nay it has frequently been observed on commons where furze grows, that wherever a bush was left untouched for some years by the inhabitants a tree has sprung up, being secured by the prickles of that shrub from the bite of cattle. So that while adjacent grounds are robbed of plants by voracious animals, some may be preserved to ripen flowers and fruit, and stock the surrounding parts with seeds which otherwise would be quite extirpated. All herbs cover the ground with their leaves, and by their shade hinder it from being totally deprived of that moisture which is necessary to their nourishment. Mosses, which adorn the most barren places, do, at the same time, preserve lesser plants when they begin to shoot, from cold and drought; as is evident in gardens, where plants are preserved in the same way. They also hinder the fermenting earth from forcing the roots of plants upwards in the spring; like what happens annually to trunks of trees, and other things put into the ground. Hence very few mosses grow in warm climates, the same necessity not existing in those places.