76 INTRODUCTION. 
examination, in which he traced all the spiral vessels longitudinally 
upwards from the ovary, as stated in greater detail in his celebrated 
work on ‘ The Various Contrivances by which Orchids are Fertilised by 
Insects,’ ed. 2 (1882), p. 235, et seg. Darwin’s remarks are illustrated 
by a figure, which I have copied below. 
Odd sepal. 
la = =— 
1 
fe) 
Side petal..__ _ Side petal. 
s 
r 
Oy, me) 
ss “ 
op 4 bo 
oO 
a 
Side sepal.-“~ “>.. Side sepal. 
Labellum or lip. 
SECTION or THE FrLowerR or AN OrcHID. (From Darwin.) 
The little circles show the position of the spiral vessels. 
ss. Stigmas; §,, stigma modified into a,,@,. Rudimentary anthers of the in- 
the rostellum. ner whorl (fertile in Cypripedium) 
A,. Fertile anther of the outer whorl; generally forming the clinandrium ; 
A,,A,, anthers of the same whorl a,, third anther of the same whorl, 
combined with the lower petal when present, forming the front of 
forming the labellum. the column. 
(Norr.—In most Orchids the odd sepal is posticous, that is, situate behind the 
rest of the flower, and next to the axis of growth. This is owing to a twist 
in the ovary which takes place during growth, and sometimes untwists after 
maturity. But in all the Satyria, in one section of Disa, and in some other 
Cape Orchids, the position is exactly reversed; that is, the ovary is never 
twisted, and the odd sepal and lip are then in their normal position, viz., 
anticous and posticous, respectively.) 
“The fifteen little circles represent so many groups of spiral 
vessels, in every case traced down to one of the six large ovarian 
groups. They alternate in five whorls, as represented; but I have not 
attempted to give the actual distances at which they stand apart. In 
order to guide the eye the three central groups running to the three 
pistils are connected by a triangle.” (Darwin, ib.) 
