178 



CEPHALANTHERA. 



[CHAP. 



grandiflora) differs from those hitherto described in 

 not possessing a rostellum, and in having the pollen 

 grains single. The flower stands upright, and the 

 labellum is formed of two portions; a base, and a 

 small triangular flap, which at first closes the tube ; 

 then turns back, thus forming a small landing place 

 in front of a triangular door, situated half way up 

 the tube ; and lastly rises up again and closes the 



FIG. 126. Listera ovata. 



entrance. The pollen mass is situated just above the 

 stigma; and while the flower is in bud, or at any 

 rate before it becomes quite open, the pollen grains 

 which rest on the sharp edge of the stigma, emit a 

 number of tubes which deeply penetrate the stigmatic 

 tissue. These serve partially, but, as Darwin has 

 shown, only partially, to fertilise the flower; he 

 suggests that the principal use of this closing of the 



