POLLINATION AND FERTILIZATION 



123 



-ti 



116. Insects as carriers of pollen. Most flowers which re- 

 quire or are benefited by cross-pollination and which are not 



wind-pollinated depend upon 

 insects as pollen carriers. It is 

 not an overstatement to say 

 that, in general, flowers seem 

 to have acquired their colors 

 (other than green) and their 

 odors as means of attracting 

 the attention of insects which 

 may serve to cross-pollinate 

 them. Insects vary greatly in 

 their efficiency as pollinators, 

 the small ones with smooth sur- 

 faces on the head, legs, and ab- 

 domen, such as ants and many 

 beetles, carrying little pollen, 

 while bees, 

 moths, and 



butterflies often carry considerable quan- 

 tities. Many bees in particular are provided 

 with a special collecting apparatus for 

 pollen (Figs. 112 and 113). Although the 

 portion which they carry to the hive or nest 

 for food is of no use for pollination, much 

 of that which is smeared over the general 

 surface of the body serves to pollinate the 

 stigmas of flowers which they afterwards 



. . , A -, , . -, .,, , . * ,, FIG. 113. Right hind 



visit. A good practical illustration of the leg of a bee $ acropis) 

 importance of insect visits is afforded by Thetibiaiscover edwith 

 the case of cucumbers grown in winter pollen of the common 

 under glass. It is found necessary to keep loos ^ S^' 

 hives of bees in the cucumber houses in 

 order to insure pollination and consequent crops of cucumbers. 

 Some idea of the number of insect visits may be gathered 

 from the fact that in a single locality dandelion flowers have 



FIG. 112. Pollen-carrying apparatus 

 of leg of honeybee 



A, right hind leg of a honeybee (seen 

 from behind and within) ; B, the tibia 

 (ti), seen from the outside, showing the 

 collecting basket formed of stiff hairs. 

 After H. Miiller 



