104 THE ORCHID REVIEW. [APRIL, 1922- 
THE GYNOSTEMIUM IN THE. GENUS DIURIS. 
NDER the above title, a paper read by Dr. R. S. Rogers before the 
Royal Society of South Australia on October 13th, 1921, has been 
published in the Society’s Transactions (vol. xlv., p. 264). The genus Diuris 
is peculiarly Australian, and does not extend to New Zealand or to any of 
the adjacent islands. ‘‘Its gynostemium,’’ remarks the author, ‘“‘is inter- 
esting, and apparently marks an important and rather primitive stage in the 
evolution of the Orchidacee. 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.” 
After describing the construction of the anther, Dr. Rogers states: “‘ Up 
to this point anther and pollinia together form an entity, entirely separate 
from other portions of the sexual apparatus.” Following a description of 
the stigmatic-plate and the position of the style, we read: ‘‘ Dehiscence is 
now about to take place, and the rostellar-disc begins to secrete freely. . . - 
The raised line or lines at the base of the lamina are exerting an increasing 
pressure against the stigmatic-plate in their progressive development, thus 
forcing the sexual elements of the flower more closely together. Dehiscence 
occurs, and for the first time union is established between the male and 
female elements of the plant. The apices of the pollinia become adherent 
to the back of the rostellar-disc. There is no caudicle. The flower expands ; 
the insect-visitor removes the ‘ viscid-disc’ together with the attached 
pollinia, and cross-pollination is then effected in the usual manner.” 
‘It is interesting in this connection,” adds Dr. Rogers, ‘ to examine the 
gynostemium of Prasophyllum, which has reached a higher degree of 
specialization than that of Diuris. Here the filament of the anther is still 
retained, but it has become adnate to the base of the style, so as to form a 
very short column.” Prasophyllum is almost exclusively an Australian 
genus, its only extension of range being to New Zealand. 
The two genera, Diuris and Prasophyllum, do not appear to have 
developed along the usually accepted lines of evolution, and these, states 
Dr. Rogers, are presumably as follows: (1) Suppression of some of the 
sexual parts and confluence of the rest to form a column ; (2) aggregation 
of the pollen into pollen-masses; (3) formation of a rostellum ; (4) appear- 
ance of a ‘viscid disc’ on the rostellum ; (5) Development of a caudicle or 
its equivalent ; (6) conversion of the pollinia from mealy or granular into 
waxy masses. Both are in possession of some of the more recently acquired 
characters of the Order, whereas in the one the column has not yet 
developed, and in the other it is apparently still in an early stage of evolution. 
Plate XXII. includes four analytical figures of Diuris longifolia. 
