INTRODUCTORY 



261 



As to its structure, we may say of a flower that it is 

 composed of the end portion 

 of a stem and of outgrowths 

 from that stem. These 

 outgrowths arise from the 

 stem just as leaves arise 

 from stems ; in fact, as to 

 origin, they are leaves. It 

 is common to speak of 

 these outgrowths as spe- 

 cially modified leaves. The 

 most conspicuous colored 

 parts of flowers are usu- 

 ally the parts called petals, 

 and petals are commonly 

 much like leaves in shape 

 as well as in the way in 

 which they arise from the 

 stem. 



A. Pollination. You 

 have learned as to leaves 

 that their character is 

 chiefly determined by 

 photosynthesis. This is 

 the principal function of 

 leaves and appears to 

 have the most to do with 

 determining their forms 

 and positions. As to 

 flowers there is also something which appears to have the 

 principal influence in determining their forms and their 



FIG. 93 D. Dogtooth violet, or yellow 

 adder's-tongue (Erythronium Americanum) . 

 One of the most graceful of spring flowers. 

 The bulb is found from four to seven 

 inches below the surface of the soil. 



