RELATION OF PLANTS TO ENVIRONMENT 7 



is often cast out of the plant in much the same form in which 

 it came into it, namely, carbon dioxide and water ; but more fre- 

 quently these substances are used over again to rebuild living 

 substance and plant food. The energy released by oxidation is 

 used by the plant in its vital processes of growth, reproduction, 

 and repair. 



The peculiar relation which nonliving matter in the form of 

 foods sustains to the living matter composing the bodies of 

 animals and plants may be expressed in various ways. Cuvier 

 and Huxley put this relation in a striking manner by comparing 

 living beings to a whirlpool. 



The whirlpool is permanent, but the particles of water which 

 constitute it are constantly changing. Those which enter it on the 

 one side are whirled around and temporarily constitute a part of 

 its individuality ; and as these leave it on the other side their 

 places are made good by newcomers. 



It is undoubtedly true that the green plant illustrates the 

 whirlpool conception more correctly than any other organism, 

 since it alone of all living forms has the power of converting 

 the simple lifeless compounds of the earth and air into living 

 matter. When we study the next topic, we shall see that animals 

 and man are not so intimately related to inorganic nature as 

 green plants are. 



THE ANIMATE ENVIRONMENT 



Most plants are intimately associated with other plants and 

 also with certain forms of animal life which affect their lives 

 in various ways and so constitute a part of their natural 

 environment. 



Thus, a plant on a lawn, in a meadow, or in a forest is closely 

 surrounded by its neighbors, which compete with it for light, 

 air, and soil space in which to expand and obtain food. Tall 

 plants shade shorter ones, and closely matted plants, like grass, 

 are likely to occupy the soil space to the exclusion of less 

 social plants. In a forest the competition of trees is always 

 evidenced by the death of those which fail to keep pace with 



