VARIATIONS IN STRUCTURE 



283 



is quite sure to blow or fall upon 

 the silk. A pollen tube must 

 grow down each thread of the 

 silk if all the ovaries are to be- 

 come well developed grains of 

 corn. If the days when the 

 pollen is ripe are rainy, the corn 

 crop is sure to be injured there- 

 by. Dry days are needed when 

 the pollen is flying. Rain 

 makes wind-pollination very un- 

 certain. The ovary of corn be- 

 comes completely filled by the 

 one seed which develops within 

 it. Thus, strictly speaking, a 

 grain of corn is not a seed ; it 

 is rather a fruit completely filled 

 by the one seed which it con- 

 tains. 



Plants with diclinous flowers 

 bear these flowers in two ways. 

 One way is to bear both stam- 

 inate and pistillate flowers 

 upon the same individual; the 

 other is to bear the staminate 

 flowers upon some individuals 

 and the pistillate flowers upon 

 others. Plants bearing both 

 kinds of flowers upon the same 

 individual are called monoecious. 

 (The word means one household.) 

 Cat- tail and corn are both 



Fig. 103. — The end of a young 

 ear of corn, the silk being exposed 

 at the end. Note that a thread 

 of the silk runs to each of the 

 young grains. 



