236 



PLANT LIFE. 



leaves adjacent are modified in form and color to adapt them 

 to securing the dispersal of the pollen by various agents, 

 especially insects. Such a shoot bearing sporophylls and 

 accessory leaves is called a flower (^[ 330). As a similar 

 aggregation of the sporophylls occurs in horsetails and many 

 club-mosses (figs. 235, 240), it is evident that the flower is 

 not distinctive of the seed plants, though it attains the highest 

 specialization among them.* 



The parts and functions of the flower of seed plants are 

 now to be discussed. 



The Flower. 



330. A flower, in its simplest form, may consist of an axis 

 bearing only a single sporophyll (fig. 243). A flower usually 

 consists of a shortened axis, the torus, bearing several sporo- 

 phylls and several accessory floral leaves (figs. 104, 244). 



9 



Fie;. 243. Fig. 244. 



Fig. 243. — A , a single flower ; B, a portion of the flower cluster of A risaruni vulgare. 



The flower is composed of one stamen only. Magnified slightly. — After Engler. 

 Fig. 244.— A flower of linden, halved ; showing a pestle-like pistil. Magnified about 3 



diam.— After Kerner. 



The sporophylls are known as essential organs, the accessory 

 leaves as the perianth and bracts. 



The essential organs are of two sorts, stamens and carpels. 

 In any flower they may be all stamens or all carpels, or may 



* It is for this reason that the term seed plants is preferred to flowering 

 plants. 



