262 EN TOMOLOGY 
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 Sphingidee. 
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 
Angrecum sesquipedale, of Madagascar, has a nectary tube 
more than eleven inches long, from which Darwin inferred the 
an 
existence of a sphinx moth with a tongue equally long, 
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 
Fic. 254. 
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 (f) leading 
up to disk and also into stigmatic chamber; /h, hood; C, pollinia; d, disk. Enlarged. 
