^o8 BOTANICAL GAZETTE [april 



o 



I 





Whether the primitive flowers were pollinated by wind or by 

 insects is uncertain. The forms of flowers w r hich preceded the 

 angiosperms were probably entomophilous. The carpels closed 

 over the ovules to form an ovary and the stigma was developed 

 to receive the pollen. The stigma and closed ovary are regarded as 

 entomophilous characters and as having been developed after the 

 visits of insects w r ere established. The origin and development of 

 entomophilous flowers, no doubt, were connected with the origin and 

 specialization of the bees, Hymenoptera w r hich adopted the habit of 

 provisioning their nests with nectar and pollen. Along w r ith the 

 acquisition of this habit, the bees developed a coat of feathery 

 hairs to which the pollen might cling, these hairs on certain parts of 

 their bodies, as the hind legs and the ventral surface of the abdomen, 

 being greatly modified to form a special pollen-carrying apparatus. 

 Thus the pollen became absolutely essential in the economy of the 

 bees. To the flowers, on the other hand, the bees became impor- 

 tant visitors, because they had to resort to flowers frequently and 

 because they were provided with a coat specially fitted to retain the 

 pollen, and at the same time exerted themselves to get the coat as 

 full of pollen as possible. 



Bees, as we know them, visit flowers both for nectar and for 

 pollen, but it is possible that the primitive bees visited flowers 

 only for pollen and that the secretion of nectar came after. 



The view has been expressed 1 that the ordinary short-tongued 

 bees can collect only viscid pollen, and that therefore they could 

 have begun to use pollen to provision their nests only after pollen 

 had become sticky in adaptation to insect pollination. Specie 

 of Chloralictus collect the dry pollen of grasses and of Plantago, 

 however, and ordinary bees collect from a considerable number of 

 flowers pollen which is so dry that it pours out as soon as it is 

 released from the anthers. So bees may have commenced to col- 

 lect pollen when only dry pollen existed. The fact that bees are 

 the most highly specialized of Hymenoptera, and the latest devel- 

 oped, does not prove, and does not seem to establish a reasonable 

 presumption, that any considerable evolution of entomophilous 

 flowers preceded their advent. 



1 Robertson, Charles, Flowers and insects. XIX. Bot. Gaz. 28:39. 1899- 



