BEES DO THEIR WORK 351 



make a more effective advertisement, challeng- 

 ing the attention of insects. The visiting bee 

 naturally alights upon the projecting keel. The 

 weight of its body presses this downward and 

 the stamens and pistils, by a springlike action, 

 are thrust out against the body of the insect, 

 scattering the pollen freely. 



Thus the stigma may become covered with 

 pollen that the bee has received from some other 

 flower while the anthers supply a new coat of 

 pollen for future distribution. 



Still a different arrangement is that of the 

 common iris. Here the anthers lie in a fold of 

 the large petallike branches of the style. The 

 stigmatic surface is confined to a little crescent- 

 shaped patch near the tip of the style branches, 

 and is protected by a thin, sacklike shield. The 

 structure of the flower is such that an insect as 

 it passes down the petals on its way to the 

 nectary, brushes against the anthers and dusts 

 off the pollen. As the insect passes out, the 

 stigma shield protects the stigmatic surface 

 completely. 



But as the insect visits another flower, its 

 pollen-covered back comes in direct contact 

 with the edge of the stigmatic shield and the 

 pollen is scraped off against the receptive 

 surface. 



