134 PLANT STUDIES 
upon the upper surface of which the stigma is developed. 
As the insect crowds its way into this narrowing chamber, 
its body is dusted by the pollen, and as it visits the next 
flower and thrusts aside the stigmatic shelf, it is apt to 
deposit upon it some of the pollen previously received. 
The story of pollination in connection with the orchids 
is still more complicated (see Fig. 133). Taking an ordi- 
nary orchid for illustration, the details are as follows. Each 
of the two pollen masses terminates in a sticky disk or 
button ; between them extends the concave stigma sur- 
face, at the bottom of which is the opening into the long 
tube-like spur in which the nectar is 
found. Such a flower is adapted to 
the large moths, with long probosces 
which can reach the bottom of the 
tube. As the moth thrusts its pro- 
boscis into the tube, its head touches 
the sticky button on each side, so that 
when it flies away these buttons stick 
to its head, sometimes directly to its 
FiG.139. A bee imprisoned d th u are t 
in the pouch (partly cut * 
away) of Cypripedium. out. These masses are then carried 
-After GIBSON. to the next fl ower an( } are thrust 
against the stigma in the attempt to get the nectar. 
In the lady-slipper (Cypripedium), another orchid, the 
flowers have a conspicuous pouch (see Fig. 137), in which 
the nectar is secreted. A peculiar structure, like a flap, 
overhangs the opening of the pouch, beneath which are the 
two anthers, and between them the stigmatic surface (see 
Fig. 138). Into the pouch a bee crowds its way and be- 
comes imprisoned (see Fig. 139). The nectar which the 
bee obtains is in the bottom of the pouch (see Fig. 140). 
When escaping, the bee moves towards the opening over- 
hung by the flap and rubs first against the stigmatic sur- 
face (see Fig. 141), and then against the anthers, receiving 
pollen on its back (see Fig. 142). A visit to another flower 
