204 SOT A xv. 



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

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

 bears the small spores pollen grains and the pollen grain 



Fig. 182. 



Diagrammatic section of a flower. A>, calyx ; A~ corolla ; f, the filament, and , the 

 anther, of the stamen ; /, 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, /', enclosing the ovule-body, S) ; em,*he embryo-sac; , germ-cell; /.?, 

 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 

 Fj ig 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. The latter corresponds to the 



cell is the genera- .... T ,, 



tiveceii. central cell of the fern antheridium. In the 



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



