574 



Insects and Flowers 



FIG. 765. Honey-bee at 

 Asclepias - flowers, with 

 legs still fast in a stigmatic 

 chamber of the flower last 

 visited. (After Stevens; 

 natural size.) 



"Each pollen-sac contains a compact mass of pollen-grains which never 

 become separated from one another, and so constitute what is termed a 

 pollinium. The two contiguous pollinia of adja- 

 cent anthers are united by horny rods which con- 

 verge upward and join with a horny dark body 

 known as the corpusculum, which is hollow and 

 has a slit along its outer face. This slit is rel- 

 atively broad at the bottom, and tapers toward 

 the top, thus forming a clip in which the feet of 

 the insects get caught. Between each pair of 

 anthers there is a deep recess closed by two vertical 

 lips which stand wider open at the bottom than 

 at the top, and the recess also narrows at the top. 

 The opening between the lips at the top stands 

 exactly beneath the slit in the corpusculum. 



"The surface of the flower is slippery, so that 

 when a bee, for instance, visits it, a good foothold 

 is not obtained until the bee slips its foot into the 

 recess between the anthers, termed the stigmatic 

 chamber. Having obtained a foothold, the bee 

 thrusts its sucking-apparatus into the hollow nectar- 

 receptacle and obtains the nectar which has invited it to the flower. When the 

 bee, however, seeks to go to another flower, its foot slips upward and becomes 

 caught in the slit in the corpusculum. A struggle 

 now ensues which usually results in the bee pull- 

 ing the two pollen-masses, united to the corpus- 

 culum, through the narrow slits at the tops of the 

 pollen-sacs; and thus laden, it seeks another flower, 

 and there slips its foot, together with the pollen- 

 masses, into the stigmatic chamber. 



"Now when the bee attempts to leave the flower, 

 the pollen-masses become tightly wedged at the 

 narrow apex of the chamber, and a hard pull is re- 

 quired to break them loose from the foot. Finally, 

 as the foot is being drawn from the stigmatic 

 chamber it catches into the corpusculum directly 

 above and pulls out a second pair of pollen- 

 masses. Thus the bee goes from flower to flower 

 and from plant to plant, repeatedly pulling pollen- 

 masses from their sacs and depositing them in 

 the stigmatic chamber. Fig. 765 is from a photograph of a honey-bee 

 gathering nectar from Asclepias-flowers. One of the hind legs is still 



FIG. 766. Cabbage-butter- 

 fly caught by legs in 

 corpuscula of two Ascle- 

 pias - flowers. (After 

 Stevens; natural size.) 



