488 



Introduction to the Study of Science 



'stillate 



such division of labor by the production of staminate and pis- 

 tillate flowers upon the same individual plant is the maize or 

 Indian corn (Fig. 154). The tassel of the corn plant, at the 

 top of the stalk, is a heavy cluster of blossoms in which are 

 the stamens with their abundant mass of pollen grains. The 

 embryonic ear is the pistil, containing a 

 large number of ovules with their silken 

 threads, which serve as styles and stigmas. 

 The pollen must be transferred from the 

 tassel to the stigmas and ovules, if the cob 

 is to produce seed or kernels of corn. Each 

 silky thread must catch its grain of pollen, 

 and when the pollen grain has grown 

 through the style to the egg-cell, the silk 

 withers or dries up at the outer end. 

 When the chances of pollen grains finding 

 their way to the silken stigma of the ear 

 are considered, the comparatively small 

 number of unfertilized ovules or missing 

 grains is astonishing. This is even more 

 striking when one finds only a few scattered 

 grains on the ears of a single isolated corn 

 plant. Why were the ovules not fertilized 

 in such a case? Did the tassel fail to 

 provide sufficient pollen ? The remarkable fact is that the 

 tassel provides enough pollen to fertilize a thousand embryonic 

 ears of corn. Then why did the pollen fail to reach the silk 

 of the ear? 



234. Close- and cross-pollination. No plant can produce 

 seed unless the pollen from the anther is transferred to the 

 stigma. By what means or agency is this transfer effected? 

 In contrast to the corn, there are a few plants, such as the pea, 

 in the flowers of which the stamens and anthers are so arranged 

 that the pollen when mature is directly transferred to the 

 stigmas. Such flowers are said to be close-pollinating or self- 



FIG. 154. The corn 

 plants, showing flowers. 



