264 



NOTES ON THE GYNOSTEMIUM IN THE GENUS DIUR/S 

 AND ON THE POLLINARY MECHANISM IN RHAJUS. 



By R. S. Rogers, M.A., M.D. 



[Read October 13, 1921.] 

 Plate XXII. 



I. On the Gynostemium of the Genus Diuris. 



The genus Diuris is peculiarly Australian, and does not 

 extend to New Zealand or to any of the adjacent islands. 



Its gynostemium is interesting, and apparently marks 

 an important and rather primitive stage in the evolution of 

 the Orchidaceae. The column or essential organ of the 

 Order, in its generally accepted sense, can hardly be said to 

 exist, as the male and female elements arise separately from 

 the receptacle of the flower, and only enjoy a brief and 

 adventitious union during the short period of maturity. 



The anther is attached to a short filament, which arises 

 from the posterior margin of the receptacle. It is placed 

 vertically, and is considerably longer than the filament that 

 bears it. It is 2-celled, each cell containing a bilobed pointed 

 or pear-shaped pollen-mass, the pollen of which is mealy. 

 The lines of dehiscence are vertical, and when ultimately 

 the integuments split and retract, they leave two cusps below 

 in which the bases of the pollinia are supported. There is 

 no clinandrium. 



Up to this point, anther and pollinia together form an 

 entity, entirely separate from other portions of the sexual 

 apparatus. 



The stigmatic-plate carries the stigma and the rostellum 

 on the upper part of its anterior face, and it is contracted 

 below into a style which takes its origin in front of, but at a 

 lower level than the filament of the anther, to which at 

 this stage it has no sort of attachment whatever. The style 

 is situated immediately over the cavity of the ovary, with 

 which it communicates by means of the stigmatic-canal. The 

 stigmatic-plate, or pistil, is approximately about the same 

 height as the anther and, like it, is quite erect. The "disc" 

 is at first an integral part of the rostellum, but as functional 

 activity approaches, separation-cells are seen to be forming 

 around it, necrosis takes place, and it is left lying loose in 

 a slot in the apex of the rostellum. 



The stigmatic-plate and the organs which it carries stand 

 immediately in front of the anther with its bulging 



