COMPOSITION AND PURPOSES OF PLANTS 3 



2. The purposes of plants. — The chief purpose 

 of every individual plant is to give rise to other 

 individuals of the same kind. In carrying out this 

 purpose the protoplasm strives constantly to perfect 

 itself, or rather its tools and organs, and to adapt 

 these more exactly to the conditions of light, mois- 

 ture, temperature, and the food supply under which 

 it is compelled to live. The manner in which the 

 living substance attempts to improve its own mechan- 

 ism and the usefulness of its tools determines the 

 form and structure of its body, and accounts largely 

 for the differences between an oak tree and a violet. 



3. Great differences among plants. — It needs but 

 the most casual glance at a field or forest to find 

 that there are many different kinds of plants in 

 it. Thus it is easily seen that some are grasses form- 

 ing a thick velvety carpet of sod on the surface of 

 the soil, while others are trees and send their round 

 trunks a hundred feet into the air. The differences 

 between the grasses and the trees are very great, but 

 all plants are not so much unlike as these two groups. 

 It will be found that there are many kinds of trees 

 and many kinds of grasses. Thus to one familiar 

 with the out-of-door world, the maple tree is not to 



