204. BOTANY. 



organs. Now the fern leaf bears the spores and the spore forms 

 the prothallium. So it is in the flowering plants. The stairen 

 bears the small spores — pollen grains — and the pollen grain 



Fig- 182. 

 Diagrammatic section of a flower. Ke, calyx ; K, corolla ; A the filament, and <z, the 

 anther, of the stamen ; p, pollen-cells, some in the anther, others on the stigma ; F, the 

 ovary, surmounted by the style, g, and the stigma, n (this ovary contains one ovule, which 

 has a single coat, i, enclosing the ovule-body, S) ; em, the embryo-sac ; E, germ-cell; /j, 

 a pollen-tube penetrating the style, and reaching the germ-cell through the micropyle of 

 the ovule. 



forms the prothallium. The prothallium in turn forms the sex- 

 ual organs. The process is in general the same as it is in the 

 ferns, but with this special difference : the prothallium and the 

 sexual organ of the flowering plants are very much reduced. 

 335. The male prothallium is reduced to the pollen grain. 

 — In fact the pollen grain is male prothallium and 

 sexual organ all in one, so reduced has it become. 

 A young pollen grain of trillium is shown in fig. 

 183. It has two cells. The entire pollen grain 

 , may be considered the antheridium, the larger cell 



Nearly mature representing the wall while the smaller cell is the 



pollen grain of tril- . 



Hum. The smaller generative cell. ihe latter corresponds to the 



cell is the genera- . 



tive cell. central cell of the fern antheridium. In the 



angiosperms it divides to form two sperm cells. These cor- 



