INSECTS AND FLOWERS 457 



receptacles for the nectar grow out and upward from the 

 bases of the stamen. 



"Each pollen-sac contains a compact mass of pollen-grains 

 which never become separated from one another, and so con- 

 stitute what is termed a pollinium. The two contiguous pol- 

 linia of adjacent 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 relatively 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 nar- 

 rows 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 foot- 

 hold, 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 an- 

 other flower, its foot slips upward and becomes caught in 

 the slit in the corpusculum. A struggle now ensues which 

 usually results in the bee pulling the two pollen-masses, united 

 to the corpusculum, through the narrow slits at the tops 

 of the pollen-sac; 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 pol- 

 len-masses become tightly wedged at the narrow apex of the 

 chamber, and a hard pull is required 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 



