272 Sargent . — Notes on the Life- History of Pterostylis . 
the gnat commenced to climb through the tunnel formed by the column 
wings, with its back towards the column. It had to struggle violently to 
get through the narrow top of the tunnel, but within three minutes after its 
capture it was free again. It settled on the window, where I easily caught 
it. After killing it with chloroform I found that it bore two pollen -masses 
on its back. 
Thrice I have seen an insect struggle through the tunnel of a P. Sargenti 
flower, but moi 4 e often these insects have shown no desire to leave their 
prison. Once I saw a dipteran hurled into a flower of P. Sargenti. It 
immediately set about sucking juice. I watched the flower for twenty-five 
minutes, at the end of which time the insect managed to escape by squeezing 
past the labellum, the flower having been damaged at one spot. I have not 
seen any other species visited. All the diptera I have seen in P. Sargenti 
flowers appear to belong to one species, and they pay no attention to other 
species of Pterostylis. The insect I saw visit a P. vittata blossom was very 
different ; I should think it belongs to a separate genus. I have several 
times seen, what seemed yet another kind of dipteran, hovering over the 
flowers of P. rtifa. A fourth kind I have seen hovering round P. nana 
flowers, and a fifth I have found dead in a flower of P. constricta. It seems 
that each species is pollinated by its own special species of dipteran, as 
careful examination of the flowers leads one to expect. Closely allied 
species are exceptions to this rule. I have found hybrids between P. re- 
flexa and P. constricta. Rodway reports hybrids between P. concinna and 
P. praecox in Tasmania, and Ewart announces the discovery of hybrids 
between P. concinna and his ‘ var. intermedia 5 of P. reflexa , in Victoria. 
My observations are insufficient to enable me to deal exhaustively with 
the pollination of these flowers, but I have formed a working hypothesis, 
which, because it seems to me so very probable, I will venture briefly to 
expound. The first time an insect is hurled into a flower it is so alarmed that 
it immediately seeks a way of escape. This it soon finds in the column-wings 
tunnel, and, as it struggles through, a load of pollen is fastened to its back. 
The attraction of the flower is great, and it is not long before the insect 
again alights on a labellum, and is a second time hurled into a flower. Its 
pollen-covered back strikes the stigma, which removes a portion of the load. 
Less alarmed on this occasion the insect probably lingers and sucks the 
intoxicating juice. A little suffices this time, and the dipteran seeks freedom 
via the tunnel. A few more flowers may be visited in a similar manner, 
but the time soon comes when the dipteran lingers in the blossom till the 
labellum falls, and then makes its exit without passing through the tunnel. 
Then, when next it visits a flower its stock of pollen will be comparatively 
small, but it will linger long, and brushing frequently against the stigma 
will coat that organ with a sufficient number of the precious grains. 
I refrain from recounting all the observations which have enabled me to 
