1 62 TEXTBOOK OF BOTANY 



184. Pollination. — The history of the formation of the 

 pollen grain within the pollen sacs, that of the macrospores 

 within the ovule (macrospore sac), and that of the develop- 

 ment of the female plant from one macrospore are so nearly 

 the same in the com and in the lily that it is not necessary 

 to repeat what was said on these subjects in the previous 

 chapter. Since pistils and stamens are borne (except in 

 rare cases) in different flowers, pollination in the com must 

 be, strictly speaking, cross-pollination ; but the pollen that 

 falls upon a particular stigma may come from a staminate 

 flower either on the same or on a different plant. Polli- 

 nation may result from the mere falling of pollen from stam- 

 inate flowers upon the silk of the pistillate flowers of the same 

 plant ; but more commonly pollination is brought about by 

 the wind, just as it is in the pine, and this usually, though 

 not always, means that the pollen from the staminate flowers 

 of one plant is carried to the pistillate flowers of another. 



185. Formation of Seed and Fruit. — The embryo and 

 endosperm begin their development in the ovule of the 

 com in much the same way that the corresponding processes 

 begin in the bean ovule. But the embryo of the com re- 

 mains small ; the endosperm continues to grow, using up 

 most of the substance of the ovule as it does so, and finally 

 the endosperm makes up the greater part of the bulk of the 

 seed. As the seed grows, the embryo is pushed to one side ; 

 it lies at the base of the upper side of the ripe seed. The 

 endosperm is full of food which will be used by the embryo 

 when the seed germinates. One great difference between 

 the bean and the com seed is in the place in which the food 

 is stored. Most of the food of the bean seed is in the seed 

 leaves ; most of that of the com seed is in the endosperm. 



The greater part of the endosperm formed in the bean 

 seed is used as food for the embryo before the seed ripens ; 

 but in the com most of the endospenn is not used in this 

 way until the seed germinates, The body of the embryo con- 



