PART 111. | THE MECHANISMS OF FLOWERS. 535 
and under favourable conditions is covered with a number of 
minute drops. A Sarcophaga which I saw seated on the under 
lip, licking these drops, flew away on my approach. But it had 
its head pointing towards the base of the lip, and if I had not 
disturbed it, it would probably not have failed to lick also the two 
black shining bodies at the base of the lip; in doing so it would 
have touched the rostellum and caused a pollinium to be cemented 
to its head. The two bodies at the base of the under lip look like 
drops of fluid, though in reality they are quite dry. They may 
be called pseudo-nectaries, and probably deceive the insect-visitors 
(5 89, 599, I.). 
382-385. ORCHIS MASCULA, O. MORIO, O. LATIFOLIA, and O. 
MACULATA.—In all these Orchids the three sepals and the two 
superior petals arch over the essential organs of the flower, while 
the inferior petal or labeilum forms a convenient alighting-place 
for insect-visitors. The labellum is prolonged backwards into a 
hollow spur, which secretes no free honey, but whose walls are 
composed of very delicate and succulent tissue. Immediately above 
the entrance to this spur stands the trilobed stigma, whose two 
inferior lobes form the true stigmatic surfaces, while the third 
superior lobe forms the rostellum. This organ, the bursicula of 
German authors, consists of a little pouch full of viscid matter, 
which projects into the mouth of the spur. The two lateral 
anthers are just visible as useless rudiments (staminodes); the 
third, and only perfect one, stands immediately above the rostellum. 
Its two loculi are separated by a broad connective, and are split 
anteriorly for their whole length by a longitudinal slit. The two 
pollinia lie within the loculi, quite unattached except at the ends 
of their caudicles, which adhere to the upper surface of the ros- 
tellum. When an insect thrusts its head into the spur, it imevit- 
ably comes in contact with the rostellum ; the membrane covering 
the latter instantly splits into an inferior portion, which curls 
backwards, and two small round disks, connected with the caudicles 
and coated abundantly with viscid matter on their lower surfaces ; 
these attach themselves to the insect’s head. The cement of the 
sticky disks quickly hardens, and when, after a short time, the 
insect withdraws its head, it takes with it the disks and the pollinia 
attached to them by their caudicles. At first the pollinia stand 
almost perpendicular to the disks, but soon, as the disks dry, the 
pollinia bend gradually forwards through an angle of nearly 90°, 
and so come into such a position that in subsequently-visited 
