VEGE TA TI VE REPR OD UC TION. 



247 



347. Sporangia.- -The anther bears from 1-12 micro- 

 sporangia upon its surface, or wholly or partly sunk in its 



P 



FIG. 262. Transverse section of the anther of thorn-apple (Datura Stramonium). 

 c, connective, with a small stele embedded in parenchyma; a, ft, <*,/, the four spo- 

 rangia, arranged in pairs showing pollen grains. When the sporangia break, the walls 

 rupture at the groove between a and /. Magnified about 25 diam. After Frank. 



tissues. In most anthers the sporangia are either 2 or 4 

 (fig. 262). When there are four they are often paired, and 

 each pair may become confluent by 

 the absorption of the portion of the 

 anther tissue between them (fig. 263). 

 This occurs about the same time that 

 the outer wall bursts in order to set 

 free the spores. Such anthers, at the 

 time of opening, are apparently two- 

 chambered. In those which contain 



Only tWO Sporangia, the tWO may Open FIG. 263. -Transverse section of 



bursted anther of a lily (Bu- 



mdependently, or they may become tomustimi>eiiatus).$von&ri& 



. have ruptured at z, so that the 



COnfllient, SO that at maturity they two pairs have each formed a 



single cavity. The connective 

 may Seem tO Constitute a Single is relatively small; in the center 



a single stele. Magnified about 

 chamber. 20 diam. After Sachs. 



348. Dehiscence.- -The opening of the chambers occurs in 

 one of three ways : by pores, by slits, or by valves, (i) A small 

 area of the outer wall is absorbed or breaks away so that the 



