Reproduction in Flowering Plants 



205 



pollen tubes sometimes develop, however, following pollination 

 from related species. The seeds produced by such crosses 



Fig. 122. Pollen grains and pollen tubes. • 5 is the two sperms or male cells, 

 and T the tube nucleus. 



often give new forms of plants that are dififerent from both 

 parents. 



After germination of the pollen, the pollen tube grows down- 

 ward through the stigma and style to the ovule, or young 

 seed. Usually this is but a short distance. In corn, how- 

 ever, the silk is the style and stigma, and the pollen tube must 

 grow several inches or a foot down the silk to the ovule below. 

 As the pollen tube lengthens, the sperms pass down the tube. 



Fertilization. Inside the ovule there is an oval, saclike 

 body which contains several cells. One of these is the egg 

 cell, or female cell. At the beginning of fertilization the 

 pollen tube grows into the ovule and discharges the two 

 sperms into the sac in which the egg cell lies. One of the 

 sperms unites with the egg cell. This union of the sperm. 



