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 anotJier flower. 

 Fertilization effected between different flowers 



is cross -f ertilization ; that resulting from the 



144 



FIG. 193. ff, POLLEN escap- 

 ing from anther; A, pollen 

 germinating on a stigma. 

 Enlarged. 



