ANTHOPHTTA. 251 



and its extension (the so-called connective) between the 

 pollen-sacs as representing a very narrow leaf upon which 

 the pollen-sacs develop as outgrowths. Sometimes the 

 stamen is broad, showing at once its leafy nature. 



474. The development of the pollen-cells is like that of 

 the spores of Pernworts and the pollen of Gymnosperms. 

 Certain internal cells (called pollen mother-cells) in the 



Fig. 148.— Diagrammatic section of a flower. C, calyx; Co, corolla; /, the 

 filament, and a, the anther, of the stamen ; p, poUen-cells, some in the an- 

 ther, others on the stigma ; 0, the ovary, surmounted by the style, s, and 

 the stigma, st (this ovary contains one ovule, which has a single coat, i, 

 enclosing the ovule-body, ) N; em, the embryo-sac ; E, germ-cell ; pt, a pol- 

 len-tube penetrating the style, and reachmg the germ-cell througli the 

 micropyle of the ovule. 



young pollen-sacs undergo division into four parts, which 

 become rounded and covered with a double coat or wall. 

 The outer coat is often much thickened, and may be 

 roughened by ridges or prickles (Fig. 149). There are 

 two nuclei in each pollen-cell: (1) the vegetative nucleus, 

 which is the remnant of the prothallium, and (3) the 

 generative nucleus, which is the homologue of an anthero- 

 zoid. 



