[i.] ORCHIDACE^E. 231 



Almost invariably insect aid is required to transport the 

 pollen from flower to flower : hence the importance of the 

 contrivances indicated above (to which Mr. Darwin some 

 years ago directed attention), to insure the proper ful- 

 filment of the important function assigned to unconscious 

 agents. 



Compare with Spotted Orchis the flowers of Pyramidal 

 Orchis (p.pyramidalis) and Bee Orchis (Ophrys apifera). 

 In Pyramidal Orchis, the two pollinia of each anther are 

 united to a single saddle-shaped disk, so that they can 

 only be removed together. In the Bee Orchis, the caudi- 

 cl.es are so weak, that when the anther-cells open, the 

 pollen-masses topple over in front and dangle opposite to 

 the viscid stigma, the glands remaining in the rostellum. 

 A puff of wind forces the suspended pollen-masses against 

 the stigma, so that in this species self-fertilization appears 

 usually to obtain. 



Remarkable modifications of these processes occur in 

 exotic species. An Orchis should not be passed by in 

 flower without experimenting upon its pollinia until the 

 mode of its fertilization be understood. 



The form of the labellum varies very much in different 

 species, assuming sometimes grotesque shapes. The 

 flowers of many tropical species are very beautiful and 

 often singularly fantastic, so that they are favourites in 

 hot-house cultivation, and are often sold at a very high 

 price. 



Many of the tropical species are called "air-plants," 

 from their being epiphytal that is, growing upon the 

 trunks of trees without becoming organically united to 

 them as parasites. They cling to the bark by long 

 greenish or white aerial roots, and absorb moisture 

 partly from the air and partly from what trickles dovs^n 

 the tree, charged with decaying organic and with inor- 

 ganic matter. The lower internodes of the stem of these 

 epiphytal Orchids often become swollen, forming what 

 are called pseudo-bulbs. 



One extremely rare British species, the Lady's Slipper 

 (Cypripedium Calceolus\ represents a Sub-type of the 

 Order, differing from the Type in having 2 lateral anthers 

 developed instead of the single posterior one, which is 

 abortive in this semis. 



