VII.] CEPHALANTHERA. 177 



When exposed to the air this drum contracts on one 

 side, and alters the direction of the pollen mass, thus 

 bringing it (as in Orchis mascula] into such a position 

 that it comes in contact with the stigmatic surface of 

 the flower to which it is carried. 



Habenaria bifolia (the Lesser Butterfly Orchis) is 

 by Bentham and other high authorities, considered as 

 a mere variety. Yet, as Darwin points out, it differs 



FlG. 125. Cephalanthera grand (flora, 



in many important particulars. The viscid disks are 

 oval ; the viscid matter itself is of somewhat different 

 character ; the drum-like pedicel is rudimentary ; the 

 stalk of the pollen mass is much shorter ; the packets 

 of pollen shorter and whiter; and the stigmatic 

 surface more distinctly tripartite. 



The genus Cephalanthera (Fig. 125, Cephalanthera 



N 



