INTRODUCTORY 



259 



stems, and leaves are alike, but as to structure they are 

 much less alike than are these other organs. Because of 

 this variety in structure it is the flowers which are prin- 

 cipally used in telling the kinds of plants apart. Often it is 

 hard to identify 

 a plant by means 

 of its stems and 

 leaves alone, but 

 it is compara- 

 tivdy easy to do 

 so when ye^ 

 have also the 

 flowers. Thus 

 there is a special 

 need to under- 

 stand flowers — 

 the need to un- 

 derstand them in 

 order to identify 

 plants. 



Many plants 

 which produce 

 seeds do not pro- 

 duce what are 

 ordinarily con- 

 sidered flowers. Grass and most trees do not produce 

 what are ordinarily considered flowers. Yet grass and all 

 trees produce seed. Evidently, if all seeds are produced 

 by flowers, we need a broader definition for the word than 

 simply " the bright-colored part of a plant." We need it 

 also because there are some bright-colored parts which are 

 not flowers at all. So, for our purpose, we may define 



JJig. 93 B. — Bluebells (Mertensia virginica). Common 

 in spring, especially along the banks 01 streams. 



