Flowers. 



187 



have long curved hairs on the hind legs which serve as 

 a sort of basket for the pollen, as shown in Fig. 103, « 

 and b. 



Having now become somewhat acquainted with the 

 equipment of butterflies and bees for deaHng with flowers, 

 it will be well to consider a few special cases showing 

 how the need of the insect for food and of the flower 

 for cross pollination are mutually satisfied. 



137. Cross Pollina- 

 tion of Datura. — Many 

 flowers possess long 

 tubes at the bottom of 

 which the nectar is 

 stored ; such flowers 

 usually have the way to 

 the nectar obstructed 

 by a constriction of 

 the tube, or by out- 

 growths in the form of 

 hairs, etc., so that only 

 those insects having 



long proboscides can reach it. The common jimson-weed 

 {Datura stramoniuin) is an excellent illustration of this. 

 The corolla is about five centimeters long, and the cavity 

 of the tube is nearly closed at about the middle of its 

 length by the insertion of the filaments there. When the 

 flower opens in the evening, it emits a strong musky odor, 

 and a large drop of nectar is already present in the 

 bottom of the tube ; so that large sphinx moths, leaving 

 the places of seclusion occupied by them during the day, 

 are attracted by the strong odor and white color of the 

 flowers. 



Flying swiftly from flower to flower, the moth thrusts 



Fig. 103. 



A, leg of a wild bee with hairs serving as baskets 

 for the collection of pollen ; B, the same laden 

 with pollen. Photomicrograph X 4. 



