Sargent . — Notes on the Life- History of Pterostylis . 269 
I am inclined to think is the homologue of the appendage found in other 
species. The two large appendages are, I believe, quite peculiar to P. 
Sargenti. They seem specially designed to part the curious curtain, which 
closes the doorway of the galea. This curtain, also peculiar to the species, 
is formed by a fringe of delicate hairs arising from near the inner edge of 
each petal, and extending half way across the doorway. The large appen- 
dages readily push the fringes aside when the labellum flies back, and thus 
clear the way for the entrance of the insect when it is hurled into the flower. 
The fringes are sufficiently elastic to regain their former position when the 
labellum falls down. 
The flowers of P . turfosa and P. barbata are closely similar, so a brief 
notice of the former will suffice for both. The lamina of the labellum is 
reduced almost to a thread. It ends in a clavate knob, and is rather 
sparsely fringed on either side with long golden hairs. Its appendage is 
a short flat rod, which looks like a continuation of the lamina back beyond 
its insertion on the claw. This strange structure leans a little away from 
the galea in the open blossom. When excited it moves back and forms 
a curtain across the entrance. 
Now in all these species the labellum is highly irritable : a very light 
touch, while it is in the ready-to-receive-visitors position causes it to fly 
back and close the lower chamber of the galea. Rough trials with the 
finger or some heavy instrument lead one to suppose that the lamina is 
sensitive all over ; but careful experiments with a bristle have convinced me 
that the sensitiveness is really localized in the appendage. Observations 
support this conclusion. I have seen insects alight on the labella of P. rufa , 
Sargenti , and vittata , and fly off again without having set the labella in 
motion. In each case the insect failed to touch the appendage, and experi- 
ment immediately after its departure showed the labellum to be in a highly 
irritable condition. The insects in question are tiny diptera. I weighed one 
like that which I saw hurled into a P. Sargenti blossom : its weight was 
just one milligram . So far as I could see it touched the sensitive spot with 
one fore-leg only, so that the pressure upon the spot must have been con- 
siderably less than a milligram. From this, some idea may be gleaned of 
how very ticklish the labellum is. The large appendages of P. Sargenti are 
not sensitive to a gentle touch. The sensitive spot lies between them at the 
base of the ridge, which I regard as a third appendage. This is one of my 
reasons for believing this ridge to be the homologue of the appendage found 
in other species. 
Having flown back, the labellum continues to keep each flower closed 
for a considerable length of time. If it be pulled forward it springs back 
immediately on release. The duration of closure varies with the species. 
In P . turfosa it is about 25 minutes, in P. reflexa about 35, in P. constricta 
