

CHAPTER XIX 



THE FLOWER — FERTILIZATION AND POLLINATION 





Fertilization. — Seeds result from the union of two ele- 

 ments or parts. One of these elements is a cell-nucleus 



of the pollen-grain. The other ele- 

 ment is the cell-nucleus of an egg- 

 cell, borne in the ovary. The 

 pollen-grain falls on the stigma 

 (Fig. 193). It absorbs the juices 

 exuded by the stigma, and grows 

 by sending out a tube (Fig. 194). 

 This tube grows downward through 

 the style, absorbing food as it goes, 

 and finally reaches the egg-cell in 

 the interior of an ovule in the 

 ovary (Fig. 195), and fertilization, 

 or union of a nucleus of the pollen and the 

 nucleus of the egg-cell in the ovule, takes place. 

 The ovule and embryo within then develops 

 into a seed. The growth of the pollen-tube is 

 often spoken of as germination of the pollen, 

 but it is not germination in the sense in which 

 the word is used when speaking of seeds. 



Better seeds — that is, those that produce 

 stronger and more fruitful plants — often re- 

 sult when the pollen comes from another flower. 

 Fertilization effected between different flowers 



is cross-fertilization ; that resulting from the 



144 



Fig. 193. — B, Pollen escap- 

 ing from anther; A, pollen 

 germinating on a stigma. 

 Enlarged. 



Fig. 194.— 

 A Pollen- 

 grain and 

 the Grow- 

 ing Tube. 



