VEGETA TIVE REPRODUCTION. 



247 



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

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



Fig. 262. — Transverse section of the anther of thorn-apple {Datura Slravwniuni'). 

 r, connecti\'e, with a small stele embedded in parencliyma ; a, /, <i, />, the four spo- 

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

 rupture at the groove between a and /. ftlagnihed about 25 diam. — .\fter Frank. 



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

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

 each pair mav become confluent by 

 the absorption of the portion of the 

 anther tissue betAveen 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 apjiarently two- 

 chambered. In those which contain 



only two sporangia, the two may open Fig. 263. -Transverse section of 

 , bursted anther of a lily (/V//. 



independently, or they may become UMusuw/v//„t„s).Sponngi!L 



. ' " , . have ruptured at z, so that tlie 



confluent, so that at maturit)' they two pairs have each formed a 



single ca\'ity. The connective 

 may seem to constitute a single is relatively small; in the center 



*" a single stele. Magnified about 



chamber. 20 di.am.-^.^fler Sachs. 



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

 one of three wa3-s : by pores, by slits, or by valves, (i) A small 

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



