April, 1908.] THE ORCHID REVIEW. 99 
ORCHIDS: THEIR STRUCTURE, DEVELOPMENT, AND 
FERTILISATION, 
Notes of a lecture given at a meeting of the Kéw Gardeners’ Mutual Improvement 
Society, held on February 17th, 1908, by Mr. R. A. Rolfe, A.L.S., and illustrated with 
lantern slides. 
(Continued from page 92.) 
PoconiA pulchella (now thrown on the screen) represents a new phase of 
development. It also is terrestrial, but there are small basal tubers, con- 
taining stores of nutriment, and solitary basal Jeaves. But it is in the 
floral structure that the great difference comes in. We have now reached 
the great suborder Monandrez, characterised by the possession of a single 
stamen—the median one of the outer staminal whorl, and equivalent to 
the staminode of Cypripedium—at the apex of the column. The pollen 
grains are powdery, and very loosely connected together by threads, the 
contents of the two anther cells being loosely aggregated together into two 
oblong pollinia, which break up at almost the slightest touch. Here a 
new organ comes into existence, called the rosetellum, which is a modifica- 
tion of the third or median lobe of the stigma—the one immediately in front 
of the anther. The other two are confluent into a single one, situated on 
the face of the column, underneath the anther. The rostellum has a 
double function, primarily that of secreting a viscid fluid, which serves to 
attach the pollinia to the insects which fertilise the flower, and secondarily 
of preventing the said pollinia from falling on to the stigma beneath. The 
viscid matter secreted by the rostellum is of quite a different character from 
that of the stigma (which it represents), for it dries very quickly on exposure 
to the air, while that of the stigma remains sticky for a long period. It has 
become modified in accordance with the special work which it has to per- 
form. The lip forms a kind of landing-stage on which the insect alights, 
and on crawling up into the flower it touches both the rostellum and the 
anther, liberating some of the viscus and the pollinia at the same time, so 
that when the insect retreats it carries them away, and on visiting another 
flower the protruding pollen comes in contact with the stigma, to which it 
in turn adheres. When the insect again retreats part of the pollen is left 
upon the stigma, and fertilisation naturally follows. 
In Epipogon Gmelinii (the next slide) a further development is reached. 
The pollen grains are much more strongly coherent, and some of them 
towards the base of each pollen mass are modified into a slender caudicle, 
which is attached to a small roundish gland by which the pollinia adhere 
to the body of the fertilising insect. The united Ponte and gland are 
called the pollinarium, a compound organ, partly derived from the staminal 
whorl, and partly from the pistillate. This coadiion represents a still 
further degree of specialisation. The vegetative —— show great 
