. Elementary biology; an introduction to the science of life. Biology. PROTECTIVE ACTIVITIES 375 instincts that have to do with the getting of food. Thus, while the ferocity of the tiger or the dog finds expression through organs that are related to food-getting, the strictly vegetarian rhinoceros or mountain sheep will fight fiercely and coura- geously with horns or hoofs. The branching horns of the deer or elk seem never to be used aggressively except against mem- bers of their own spe- cies, as when two males are in combat. 413. Shedding of leaves. The dropping of leaves in the autumn, whil
. Elementary biology; an introduction to the science of life. Biology. PROTECTIVE ACTIVITIES 375 instincts that have to do with the getting of food. Thus, while the ferocity of the tiger or the dog finds expression through organs that are related to food-getting, the strictly vegetarian rhinoceros or mountain sheep will fight fiercely and coura- geously with horns or hoofs. The branching horns of the deer or elk seem never to be used aggressively except against mem- bers of their own spe- cies, as when two males are in combat. 413. Shedding of leaves. The dropping of leaves in the autumn, while it does not in- volve movements like those of muscles, may properly be considered a protective The shedding of leaves seems to be related to the water factor as well as to the temperature factor, which we usually associate with the change of seasons. As the au- tumn advances and the water in the soil becomes Fig. 196. Insect galls It is probable that by the formation of such galls many plants are really protected against serious in- jury, although many of the galls may simply represent the behavior of protoplasm when injured in a certain way, rather than a useful way of behaving. It is in- teresting to note that the galls are always specific. Thus, both of these galls are on the same species — the white oak {Qitcrciis alba)—but are produced by different species of insects: i, hy Bior/iiza fortiLornis; 2, by Holcaspis globulus scarcer, transpiration is interfered with. Evaporation from the leaves, however, continues so long as there is water in the cells. If the loss of water cannot be compensated by the absorption of the roots, the live cells of the plant must suffer injury. The leaf cells are the first to be affected. The loss of the leaves prevents the complete drying up of the plant, and it also prevents the freezing of live cells (see Fig. 195). The relation of water to the fall of the leaf has been determined Please note that these images are e
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