BEES DO THEIR WORK 349 



A simple and effective method of guarding 

 against self-pollination we have seen illustrated 

 in the common geranium (Pelargonium). 



When the geranium flower first opens, a little 

 cluster of anthers may be seen on the tip of the 

 erect filament in the center of the bright, showy 

 flower. At this stage the undeveloped stigma lies 

 closely folded up and wholly unreceptive among 

 the stamens. But soon after the pollen has been 

 shed or gathered, the anthers drop off; then the 

 stigma spreads out its five receptive lobes from 

 the tips of the connecting filaments, and is ready 

 to receive pollen from another flower. 



In the snapdragon (Antirrhinum), and in 

 many other related plants, the anthers lie along 

 the roof of the corolla tube, where they are 

 brushed by insects that pass down the tube 

 in search of nectar. The stigma holds a similar 

 position, but is farther out toward the mouth of 

 the tube. The stigma is a very interesting 

 structure; it is composed of two flattened lips, 

 which respond to the slightest touch. 



When a bee, after visits to other flowers, 

 enters the tube, the hairlike appendages on its 

 back brush against the lower lip of the stigma, 

 and the irritation causes the lips to close quickly 

 and tightly together, coming thus in contact with 

 and scraping the pollen-dusted back of the bee. 



