FUNCTIONS OF PLANTS 283 



them. Plants must feed, and for this purpose they must 

 have organs of nutrition. Then, if the species, or kind, 

 of plant is to survive, there must be organs for the pro- 

 ducing of new members of the species; these are the 

 organs of reproduction. Animals, as well as plants, must 

 carry out these two elementary processes successfully, if 

 they and their kind are to continue on the earth. The 

 higher plants carry out the process of nutrition in their 

 roots, stems, and leaves, and that of reproduction in 

 flowers and seeds. 



But the plant, well as it may be fitted to live, is of no 

 consequence by itself. It must have proper surroundings, 

 such as soil, sunlight, air. The presence of other plants, 

 of the same or a different kind, and of animals, also 

 affects greatly the future of the plant. We call all these 

 surroundings of an organism, which help or hinder its 

 development, the environment of the organism. 



It requires only a little observation to show us that the different 

 kinds of plants have become accustomed to certain environments. 

 Some do best in shady places, others in sunshine; some prefer sandy 

 soil; some, clay; some, humus. We say that each species, or variety, 

 has adapted itself to, or fitted itself for, its environment. 



All the conditions, or influences, of the environment call out some 

 action on the part of the plant. We call the environment's influence 

 the stimulus (plural, stimuli; we have the same meaning in ''stimu- 

 late"); the action of the plant we call its reply, or response, to the 

 stimulus. Thus, we say that light is a stimulus to our eyes, and sight 

 is the eyes' response. Light is a stimulus to the sunflower, too; the 

 turning of the sunflower toward the light is one way in which it re- 

 sponds to light. The environment is not always quite the same; so 

 plants are successful or unsuccessful according as they have, or have 

 not, developed parts to meet the conditions and changes in their envi- 

 ronment. 



