NATURAL SELECTION 75 



humming-birds, the countless butterflies, the ants, the lizards, 

 and the snakes. 



Are there crises in the life of a plant as in that of an animal ? Crises in 

 No doubt there are occasional emergencies e.g., extreme cold p i ants 

 or a drought, when even the deepest roots can find no moisture 

 and the air contains but little. But, speaking generally, a purely 

 vegetable existence is not marked by the ups and downs that 

 come in animal life. A plant can store up food, or rather its 

 products. A deciduous tree, after the leafless time of winter, is 

 able suddenly to cover itself with foliage. In its bulb a hyacinth 

 has a great depot of nourishment that enables it to be ready at 

 the first appearance of spring. An animal, a bird or mammal at 

 any rate, is an engine that requires constant stoking up. Hiber- 

 nation is rather a proof of this than otherwise. So small is the 

 store of nourishment that a marmot can put by, that, to make it 

 last any time, he must husband it by remaining torpid. Still, 

 even among plants, there are terrible crises, though, as a rule, 

 they do not affect well-established individuals. In a tropical 

 forest all the ground is occupied. There are the giant trees and 

 creepers clinging to them and hanging in festoons. There is 

 an undergrowth of smaller trees, and often, under that, a third 

 growth of comparatively dwarf trees, while perhaps the ground 

 is covered with selaginella. 1 At length one of the giants falls 

 and carries destruction with him. Light is let in, and among 

 the seeds of all the neighbouring trees there is a struggle, as in 

 the Black Hole of Calcutta, to get near to the window. For 

 through that window in the dense canopy comes the sunlight 

 that to a vegetable is the very elixir of life. For years and years 

 the trees round about have been producing seeds by the thousand 

 or million, none of which, unless transported by birds or other 

 carriers, had any chance of growing. Now at last has come an 

 opportunity. In the opening numbers of young trees will spring 

 up, but only a very small number will survive. The rest will 

 be shut out from the light by quicker-growing or more vigorous 

 competitors. Such things may go on in English woods ; but man 

 interferes a great deal with the processes of nature, or, to put it 



1 Dr A. R. Wallace's Tropical Nature, p. 34. 



