262 



ENTOMOLOGY 



and other pollenizing insects ordinarily visit in succession sev- 

 eral flowers of the same kind. 



Orchids. The orchids, with their fantastic forms, are really 

 elaborate traps to insure cross pollination. In some orchids 

 (Habenaria and others) the nectar, lying at the bottom of a 

 long tube, is accessible only to the long-tongued Sphingidse. 

 While probing for the nectar, a sphinx moth brings each eye 

 against a sticky disk to which a pollen mass is attached, and 

 flies away carrying the mass on its eye. Then these pollinia 

 bend down on their stalks in such a way that when the moth 

 thrusts its head into the next flower they are in the proper 

 position to encounter and adhere to the stigma. The orchid 

 Angrcpcum sesquipeftale, of Madagascar, has a nectary tube 

 more than eleven inches long, from which Darwin inferred the 

 existence of a sphinx moth with a tongue equally long, an 

 inference which proved to be correct. 



Milkweed. The various milkweeds are fascinating subjects 

 to the student of the interrelations of flowers and insects. The 

 flowers, like those of orchids, are remarkably formed with 



FIG. 254. 



B 



Structure of milkweed flower (Asclepias incarnata) with reference to cross pollina- 

 tion. A, a single flower; c, corolla; h, hood; B, external aspect of fissure (/) leading 

 up to disk and also into stigmatic chamber; h, hood; C, pollinia; d, disk. Enlarged. 



