80 WILD FLOWER PRESERVATION 



anthers have shed their golden pollen dust, and 

 the pistil's style has lengthened so that the lit- 

 tle stigma has pushed the pollen up to the 

 mouth of the corolla tube, where insects may 

 easily find and carry it off to other robin's 

 plantain flowers (see Fig. 9) . 'You must now 

 take a third floret still farther from the center 

 of the disc. "What's happened?" you ask. 

 The pollen has gone, the stigma seems to have 

 gone too (Fig. 10) ; but in its place two arms 

 are outspread, two stigmas instead of one. 

 There always were two stigmas, but they were 

 folded together like hands, palm to palm, and 

 the sticky, stigmatic surface was inside. This 

 elaborate floral mechanism ensures cross-ferti- 

 lization, and prevents or lessens the chance of 

 self-fertilization. As long as the floret's own 

 pollen was within the corolla tube the stigmatic 

 surfaces were enclosed and protected. To en- 

 able insects to gain access to this pollen and to 

 carry it off to other flowers the style length- 

 ened, and the protected stigmas pushed it up 

 and out as a sweep's brush pushes soot out 

 from the chimney. Then when the pollen had 

 been carried away came the pistil's turn, and 



