CHAPTER XXII. 



REPRODUCTION — {continued). 



SEXUAL REPRODUCTION. 



I. The essential feature of the sexual reproduction of plants 

 and animals also, is the fusion of two special kinds of cells, 

 namely, a male reproductive cell, and a female reproductive 

 cell, which after complete coalescence or commingling of parts, 

 give rise to a single cell capable of growing into a new organism. 



In the very exceptional cases of parthenogenesis, a female cell 

 develops into a new plant without previously uniting with a 

 male cell ; as a rule, however, neither a male cell nor a female 

 cell is capable of further development by itself, and it is only 

 after the process of fertilisation or union of the male cell with 

 the female cell that the latter grows into a new individual plant. 



The two uniting cells, or gametes as they are termed, are 

 produced in special reproductive organs which vary very much 

 in different divisions of the Vegetable Kingdom. We can, at 

 present, only deal with the sexual cells and reproductive organs 

 of ordinary flowering plants. 



The reproductive organs oi these plants form the essential 

 parts of flowers as mentioned in chap. vi. ; the stamens are 

 the male organs and the carpels the female organs of the 

 plant. 



The male reproductive cell is enclosed within the pollen-grains 

 produced in the stamens ; the female reproductive cell lies with- 

 in the ovule as explained below. 



2. Structure and Germination of the PoUen-G-rain. — Pollen- 

 grains vary much in form, size and colour : they are, howevei, 



c6g 



