V EG ETA TIVE REP ROD UCTION. 



249 



ments only, or by their anthers only, or throughout their 

 whole length. Union with the pistil or pistils is rather un- 

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

 The union of stamens may be real or apparent. They may 

 develop independently and later 

 cohere by their adjacent edges 

 (fig. 266). Or they may begin 

 development separately 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. When 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, except by studying 

 their development. When sta- 

 mens branch a single fundament appears, on which later arise 

 smaller knob-like elevations, 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 various, being round, ovoid, or even 

 angular, with the surface smooth, grooved, or roughened with 



Fig. 266. — The stamens of one of the 

 sunflower family {Cosmos bij>in- 

 natus). A, stamen tube formed by 

 five stamens coherent by their an- 

 thers around the style ; the fila- 

 ments 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. Mag- 

 nified about 7 diam. — After Baillon. 



