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 

 eyes, and the pollen masses are torn 

 out. These masses are then carried 

 to the next flower and 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 



Fig. 139. A bee imprisoned 

 in the pouch (partly cut 

 away) of CypripediutJi. 

 — ^After Gibson. 



