26 NATURE STUDY. 



may fill the air with clouds of yellow dust, and the single 

 or double insect borne pollen-sacs of the higher orchids, 

 there is a difference as instructive as it is amazing. 



The pollen of orchids has, in fact, become specialized to 

 such an extent that it differs from ordinary pollen as much 

 as orchid flowers differ from ordinary flowers. It has been 

 specialized as to consistence and coherence and viscidity, 

 and the sacs containing it have been specialized as to shape 

 and location, and in some cases have even developed the 

 power of automatic movement. The orchid not only takes 

 pains to secure pollen from another flower but it tries as 

 carefull}^ to prevent its own pollen from coming in contact 

 with its own stigma, as if that in itself w^ould be sure to in- 

 jure it. The way in which both these ends are secured is 

 finely illustrated in the two species of lady-slipper described 

 in the last article. 



The slipper or pouch is in reality an insect trap, which 

 the insect may enter easily but from which he cannot de- 

 part until he has paid toll by doing his jailer's bidding. 

 Take now the case of the yellow lady-slipper, where the lip 

 is actually shaped like a babies sock. This lip is, roughly 

 speaking, spheroidal in shape and there is a fine large open- 

 ing in the top. Attracted by something, probably the odor 

 of a nectar-like secretion within, the insect boldly enters. 

 He then finds himself on the concave inner surface of a 

 golden sphere, delights himself with such sweets as he may 

 find there, and when satiated tries to get out the same way 

 he got in. There is the great opening in the top, through 

 which he may see the sky and the sun. Surely here must 

 be a free exit. So he starts to crawl out. But the surface 

 near the opening is very slippery. There is nothing to 

 cling to and he falls back. Not daunted he tries again. 

 Perhaps he is able, in spite of slipping, to reach the ver}' 

 edge of the sky-light. But here he encounters a fresh ob- 

 stacle. All around the edge there is a fence, the top of 



