THE DICOTYLEDONES 



1885 



bent so that the edges he close together and in the middle of its lower 

 border is a wedge-shaped sht. Two pollinia, lying in the adjacent loculi of 

 two different anthers, are attached by bands to this clip. 



Nectar is secreted abundantly and when a fly tries to suck the nectar 

 secreted in one of the coronal pits situated immediately below one of the 

 clips, its extended proboscis, beset with erect bristles, will be guided up- 

 wards into the slit between adjacent anther wings until it is held fast in the 

 clip. When the insect withdraws its proboscis with a jerk, it pulls away 

 the clip and the two pollinia attached to it. At first the pollinia are sharply 

 divergent, but as the bands dry, they become closely appressed. Should 



Fig. 1797. — Asclepias curassavica. Pollination. A, Longitudinal section of 

 flower. B, Insect with pollinia attached to its legs. 



such an insect visit another flower, the pollinia are readily thrust into one 

 of the slits and guided by them will slip into the stigmatic chamber, thus 

 effecting cross-pollination, for, on this occasion, when the insect withdraws 

 its proboscis the pollinia are torn away from the band connecting them to the 

 clip, while at the same time a new clip with fresh pollinia becomes fastened 

 on to the proboscis. Two-winged flies allied to the house fly are the 

 most efficient and are the chief agents of pollination. 



Species of Asclepias (Ing. 1797), e.g., A. syriaca, are adapted to bee 

 pollination. Here it is the legs rather than the proboscis which become 

 caught by the clips. A bee probing for nectar tends to slip on the smooth 

 flower till its legs get a firm grip on a slit. When it lets go and draws up its 

 legs, the claw is guided upwards in the slit, and it carries away the clip 

 with the attached pollinia. In visiting another flower the pollinia become 



