CHAPTEE XIII 



THE FLOWER 



119. General characters. — In general the flower may be 

 regarded as a modified branch of the sporophyte stem bear-« 

 ing sporophylls and usually floral leaves. Its representa- 

 tive among the Pteridophytes and Gymnosperms is the stro- 

 bilus, which has sporophylls but not floral leaves. Among 

 Angiosperms it begins in a simple and somewhat indefinite 

 way, gradually becomes more complex and modified, until 

 it appears as an elaborate structure very efiicient for its 

 purpose. 



This evolution of the flower has proceeded along many 

 lines, and has resulted in endless diversity of structure. 

 These diversities are largely used in the classification of 

 Angiosperms, as it is supposed that near relatives are indi- 

 cated by similar floral structures, as well as by other fea- 

 tures. The significance of these diversities is supposed to 

 be connected with securing proper pollination, chiefly by 

 insects, and favorable seed distribution. 



Although the evolution of flowers has proceeded along 

 several lines simultaneously, now one feature and now 

 another being emphasized, it will be clearer to trace some 

 of the important lines separately. 



120. Floral leaves. — In the simplest flowers floral leaves 

 do not appear, and the flower is represented only by the 

 sporophylls. Both kinds of sporophylls may be associated, 

 in which case the flower is said to be perfect (Fig. 195) ; or 

 they may not both occur in the same flower, in which case 

 one flower is sta7ninate and the other pistillate (Fig. 196). 



218 



