MORPHOLOGY OF LEAVES AND FLOWERS 



617 



cells to be fertilized. The other nucleus of the pollen grain pro- 

 duces two small nuclei which are called sperms. These sperms 

 pass down the pollen tube to the embryo sac and fertilize the egg 

 and endosperm nucleus. 



THE PISTIL AND ITS FUNCTION IN SEED PRODUCTION. 



A flower may have one or more pistils which occupy the center 

 of the flower. They are the last to appear, since the order of 

 development is usually sepals, petals, stamens, and pistil. 



Fig. 478. 



Iris with petal-like stigmas. 

 (After Thome.) 



A complete pistil consists of three parts — the expanded base 

 which bears the seed and is called ovary (or "egg-case") ; the ex- 

 panded portion at the top, or the stigma; the portion that connects 

 the ovary and stigma, the style. 



The style is not an essential part of the pistil and may be absent 

 without disturbing the function of the pistil. 



The stigma has on its surface many minute papillae which re- 

 tain the pollen and excrete a sweetish, sticky fluid which serves 

 as a nourishment and stimulant for the pollen grain. 



