V EG ETA TIVE KEPROD VCTION. 



249 



ments only, or Ijy tlieir anthers oul)-, or throughout tlicir 

 whole length. Uiiioii wilh the pistil or pistils is rather un- 

 common, but union with the corolla or calyx is very frequent. 

 The union ofstamcns may be real or apparent. They may 

 develop independentl)' and later 

 cohere by their adjacent edges 

 (fig. 266). Or the)' may begin 

 development sejiarately and be 

 subsequently raised by the growth 

 of a ring of tissue of the torus 

 (^360), so that the free portions 

 arise from the top of a shorter or 

 longer tube, ^\'hen the stamens 

 and corolla, arising independently, 

 are carried up together by the 

 growth of such a zone of the axis, 

 the stamens appear to arise from 

 the surface of the corolla (fig. 

 267}. 



350. Branching. — The sta- 

 mens frequently branch, and this 

 is difficult to distinguish from the 

 displacement by basal growth just 

 described, excejjt by studying 

 their development. When sta- 

 mens branch a single fundament appears, on which later arise 

 smaller knob-like ele\"ations, the fundaments of the branches, 

 each with its own growing point. (See figs. 268, 269, 270; 

 also * 171 and figs. 146, 166 on branching of leaves, of 

 which this is only a special case. ) 



351. Pollen grains. — The microspores produced in the 

 sporangia of the stamen are at maturity single cells. Their 

 forms and walls are \"arious, being round, ovoid, or even 

 angular, with the surface smooth, groo\'ed, or roughened with 



Fig. 2(/i, — Tlie stamens of one of tlie 

 sunlliiwer faniilv ^Cos'iws /n/'in- 

 n.ifns). A , stamen tube fornied by 

 live stamens coherent by their an- 

 tliers aronnd the style ; the fila- 

 nieiits with a tuft of hairs about the 

 middle. B, the same, but stamens 

 only ; the tube has been slit along 

 one side and opened out flat ; seen 

 from the inside. Connective pro- 

 longed : dehiscence by slits. I^fag- 

 nificd about 7 diam.— After HaiUon. 



