VSGS: TA 7WE REP ROD UCTION. 



203 



lengthwise of the anther (fig. 164); or (3) the break occurs 

 along a line considerably curved, and the flap (valve) thus 



Fig. 161. — Transverse section of the anther of thorn-apple {Datura Sirantonium). 

 c, connective, with a small stele embedded in parenchyma; a,/, «,>, the four spore 

 cases, arranged in pairs showing pollen grains. When the spore cases break, the 

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



loosened curls up or lifts so as to allow the escape of the 

 spores (fig. 165). All three methods are dependent upon 

 some special structure of the wall of 

 the spore case at the lines of rupture 

 (figs. 161, 162). 



290. Union. — The stamens are 

 not infrequently united with one an- 

 other or with some of the neighbor- 

 ing leaves of the flower. They may 

 be united to one another by their fila- 

 ments only, or by their anthers only, 

 or throughout their whole length. 

 Union with the pistil or pistils is 

 rather uncommon, but union with 

 the corolla or calyx is very frequent. 

 The stamens also branch just as 

 ordinary leaves do. 



291. Pollen grains. — The spores produced in the spore 

 cases of the stamens are of various forms, being round, 



Fig. 162. — Transverse section of 

 bursted anther of a lily {Buto- 

 Tnits umbellatus). Sporangia 

 have ruptured at z, so that the 

 two pairs have each formed a 

 single cavity. The connective 

 is relatively small ; in the cen- 

 ter a single stele. Magnified 

 about 20 diam.^ — After Sachs. 



