POLLINATION 417 



848. Some of the orchids present the most remarkable 

 adaptations for pollination through the agency of insects. 

 In Arethusa the pollen is contained in a receptacle which 

 opens by a lid. This lid is torn open by the insect in its 

 efforts to back out of the flower, and the pollen falls upon its 

 back. In backing out of the flower, however, the insect first 

 brushes against the stigma, which would then be pollinated, 

 provided the insect had previously visited another similar 

 flower. 



849. The little showy orchid (Galeorchis) has two pollen masses 

 (pollinia) which lie in the throat of the corolla, one on either 

 side of the stigma. Each pollen mass consists of pollen grains 

 bound together by threatts and is attached to a sort of stalk 

 which ends in a viscid disc. The polliriium is enclosed in a sack, 

 but the disc is exposed and projects forward toward the entrance 



o the corolla. When an insect thrusts its head into the throat 

 of the corolla, as it must in order to reach into the deep nectary, 

 the discs of the pollinia adhere to the eyes or some other part 

 of the head and are withdrawn when the insect leaves the 

 flower. The position of the pollinia is now such that when 

 another similar flower is visited by the insect the pollinia are 

 thrust directly upon the broad stigmatic surface. 



850. The lady slipper (Cyprepedium) has again another 

 device. The large cup formed by the "lip" of the corolla is 

 readily entered, but exit is difficult because of the way the edges 

 are inrolled. A small opening on either side of the column, 

 which bears the two anthers and the stigma, attracts the atten- 

 tion of the prisoner and he forces his way through one of these. 

 In doing so he must creep under the column and his back 

 brushes against the stigma first and then the anther. If he 

 had previously visited a similar flower some of the pollen on 

 his back would now adhere to the stigma and^a new supply 

 of pollen would immediately be obtained as he passes the anther, 

 for the next flower visited. 



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