256 



GKADATION Oi< ORGANS. 



C'HAl'. IX. 



0. mascula the two sides of the hood partly adhere ; 

 and in 0. 2iyram{daj:s and in Aceras it is converted 

 into a solid ridge. These facts arc intelligible only 

 on the view, that, whilst the two discs were gradually 

 brought together, during a long series of generations, 

 the intermediate portion or summit of the rostellum 

 became more and more arched, until a folded crest, 

 and finally a solid ridge was formed. 



Ficr. 37. 



KOSTELLUM OF CaTASETOTI. 



<m. antenua3 of I'ostellum. 

 d. viscid disc. 



pcd. pedicel of rostellum, to which 

 the pollen-masses are attached. 



Whether we compare together the state of the ros- 

 tellum in the various tribes of the Orchidea?, or com- 

 pare the rostellum with the pistil and stigma of an 

 ordinary flower, the differences are wonderfully ffi'oat. 

 A simple pistil consists of a cylinder surmounted by 

 a small viscid surface. Now, see what a contrast the 

 rostellum of Catasetum, when dissected from all the 

 other elements of the column, presents; and as 1 

 traced all the vessels in this Orchid, the drawing may 

 be trusted as ap})roximately accurate. The whole organ 



