POLLINATION AND FERTILIZATION 



149 



found a body shaped somewhat like a grain of wheat (fig. 134, 

 C and .Z)). This body, the corpusculum, is attached at each 

 side to one pollen mass of each of the two adjacent anthers 

 (fig. 134, B and (7). Along the corpusculum runs a slit which 

 gradually narrows toward the upper end and thus acts as a 

 clip, holding firmly any small object that is drawn into it. As 

 the exterior of the flower is smooth and slippery, the only way 

 in which an insect can hold itself in place upon it is by insert- 

 ing its claws in the slit of a corpusculum. When the insect 



corp 



FIG. 134. Flower of the milkweed (Asclepias) 



A, general view ; B, side view of flower after removal of the sepals, petals, and 

 nectar-hearing organs ; C, pollen masses with attached clip ; D, pollen masses 

 with clip attached to foot of a hee; cal, calyx; co, corolla ; ch, stigmatic cham- 

 her, inside of which is the stigma ; corp, corpusculum, or hody to which the 

 pollen masses are attached, acting as a clip; loc, locule, or pollen chamher of 

 anther; po, pollen mass. All somewhat enlarged. A and C, after Prautl; B, 

 after Herman Mttller ; D, after Kerner 



attempts to fly away, it drags the corpusculum and attached 

 pollen masses with it, suspended by one or more claws 

 (fig. 134, jD), or sometimes it is held fast and dies. Hairy 

 insects, like bumblebees, often carry away many pollen masses 

 on the hairs of the under surface of the body (fig. 135). If 

 the insect escapes from the flower and visits another, when 

 it thrusts its foot through a corpusculum slit of the second 

 flower the pollen masses already attached to the foot become 

 torn away. The pollen masses thus detached are left in con- 

 tact with the stigma of the second flower, and in this way most 

 effectively secure cross-pollination. 



