246 



TAKING UP OF POLLEN BY INSECTS. 



sap. Sometimes little drops of nectar are also secreted by the cells composing these 



hairs. Certain small bees of the genus Andrena are in the habit of entering the 



cavity to feast on the hairs. Three ways are open to them, viz. the two small 



orifices in the background on either side of, and close to, the column, and the large 



oval opening in the middle of 



the slipper and in front of the 



column. They choose the last 



and slip under the broad, rough 



stigma to the bottom of the 



slipper where they feed on the 



succulent cells of the hairs. After 



a time they wish to escape into 



the open air again, but that is 



not so easy. The edges of the 



large central opening are inflected 



(see fig. 267 ^), and so fashioned 



as to be unscalable, and the bees 



have no choice but to make 



use of one of the two little 



exits at the back of the slipper. 



Fig. 266. — Contrivances for loading insects with pollen. 



1 Flower of an Iris (Iris Germanica), with three segments of the perianth reflexed and three erect. On each of the former la 

 a strip of yellow hairs which stand out conspicuously from the violet background of the perianth-segment, and serves as 

 a guide to insects entering the honey-containing tube of the perianth. 2 Upper half of the perianth-tube showing the 

 three passages leading to the honey. Above each passage is a stamen with a long, linear anther facing outwards, and 

 arching over each stamen is one of the three bi-lobed petaloid stigmas. The perianth-lobes have been removed. 



Even through these escape is not altogether easy, the bees being obliged to squeeze 

 through the narrow opening. The result is that one shoulder brushes against the 

 soft, viscid pollen of the anther which forms the inner border of the orifice. The 

 last act in the story is the entrance of the insect with its shoulder covered with 

 pollen into another Cypripedium flower, whose rough stigma is thereupon imme- 

 diately besmeared with pollen. 



