256 GRADATION OF ORGANS. CuAP. IX. 



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

 and in 0. pyramidalis and in Aeeras it is coinrerted / 

 into a solid ridge. The^e facts are inlmlgi-ble only' 

 jQa-the^vie\v,_thaty-whiIst 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. ^ 



Fig. a?. 



Rostellum op Oatasetiih. 



an. antenniE of rostellum. I ped. pedicel of rostellum, to which 



d. viscid disc. I the pollen-masses are attached. 



Whether we compare together the state of the ros- 

 tellum in the various tribes of the Orchideae, or com- 

 pare the rostellum with the pistil and stigma of an 

 ordinary flower, the differences are wonderfully great. 

 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 I 

 traced all the vessels in this Orchid, the drawing may 

 ho, trusted as approximately accurate. The whole organ 



