458 



THE ANIMALS AND MAN 



B 



the bee goes from flower to flower and from plant to plant, 

 repeatedly pulling pollen-masses from their sacs and de- 

 positing them in the stigmatic chamber. Fig. 236 is from a 

 photograph of a honey-bee gathering nectar from Asclepias- 

 flowers. One of the hind legs is still in the stigmatic cham- 

 ber of the flower, which the bee has just deserted." 



Hive-bees, although common 

 visitors to Asclepias, are really 

 hardly strong enough to insure 

 pulling loose from the flowers, 

 and many of them besides num- 

 erous flies and small butterflies, 

 get caught and die in the flower- 

 heads. Robertson has noted 

 nine species of insects thus killed 

 by Asdepios cornuti. Bumble- 

 bees and large wasps and large 

 butterflies are the most certain 

 milkweed pollinators. 



Still another markedly differ- 

 ent kind of specialization to 

 FIG. 237. Flower of Aristolo- effect cross-pollination by insects 

 chia demaiitis in longitudinal is that shown by many Araceae 



section: A, before fertilization and Aristolochiace ^ The flow . 

 by little fly; B, after fertihza- . 



tion; p, pollen-masses; s, stig- er (fig. 237) in these plants 

 ma; 6, bristly hairs; wb, with- consists of a long tubular peri- 

 out bristly hairs. (After H. anth ( the) w j th a con striction 

 Muller.) 



near the base, the narrow open- 

 ing into the cavity below being nearly closed by stiff down- 

 ward-pointing hairs, so as to make a sort of floral eel-trap. 

 It really is an insect-trap; small flies crawl down the long 

 tube and through the narrow opening in search of nectar; 

 but when ready to return find themselves imprisoned by 

 the downward-pointing hairs. After a while the stigmas, 

 which mature before the anthers and have likely been polli- 



