194 



GROWTH AND WORK OF PLANTS 



Fig. 147. 

 Cypripedium. 



keel it opens, the stamens fly upward and throw the pollen, 

 already lying in a loose mass above the anthers, on to the 

 body of the insect. When it visits another 

 flower in which the stigma shows above the 

 keel and is receptive, some of the pollen on 

 its body is brushed on to the stigma. In 

 the canna flower the pollen is shed from the 

 anther (while the flower is still closed) and 

 glued on to one side of the broad style 

 right by the side of the stigmatic surface 

 but not on it. As the flower partly opens, 

 bumblebees alight on the lower petal 

 (labellum), which suddenly curves down- 

 ward, taking the bee far below the stigmatic 

 surface. As the bee enters the flower it brushes against the 

 pollen mass and removes some of it, but as it was immediately 

 lowered it could not rub this pollen on to the stigma while it 

 was taking the nectar. But as it visits the next flower, when 

 it first enters some of the pollen 

 from the previous flower is 

 brushed off on the stigma. In- 

 teresting experiments can be 

 made on some of the orchids 

 grown in green-houses with a 

 lead pencil or other slender- 

 pointed instrument to imitate the 

 movement of the proboscis of an 

 insect. Some of the native 

 orchids can be used to demon- 

 strate the methods of cross-polli- 

 nation. 



310. Flowers constructed to 

 lead the insect in at one point 

 and out at another. Some of 

 our native species illustrate this. One species of the lady- 

 slipper (Cypripedium) is shown in fig. 147. The insect enters 



Fig. 148. 



Section of flower of Cypripedium. st, 

 stigma; a, at the left stamen. The insect 

 enters the labellum at the center, passes 

 under and against the stigma, and out 

 through the opening b, where it rubs 

 against the pollen. In passing through 

 another flower this pollen is rut ' 

 the stigma. 



off on 



