CHAPTER XX. 

 METHODS OF POLLINATION. 



292. The necessity of pollination. Pollination is the trans- 

 ference of the pollen from the anthers to the stigma of the pistil. 

 Here the pollen grain germinates. The pollen tube then passes 

 down through the style, enters the ovule, and carries the sperm 



Fig. 136. 

 Photomicrograph of pollen grains of sunflower, highly magnified. 



cell (the fertilizing element) to the egg cell. The union of the 



sperm cell and egg cell brings about the fertilization of the egg 



cell, which is necessary (except in rare cases) in order that the 



egg may develop into the embryo and bring about the formation 



of the seed. There are many different devices, or mechanisms, 



in the flower structure for bringing about pollination.* 



* See Darwin, Cross fertilization, etc. 



182 



