METHODS OF POLL1NA TION 



193 



Fig. 145- 



Two flowers of common sage, one of them visited 

 by a bee. After Lubbiock. 



or other object. The common garden sage (Salvia) presents a 

 very peculiar structure and movement of the stamens (fig. 145). 

 As the insect enters the flower it pushes against the lower sterile 

 anther lobe, which causes the connective to swing on its hinge in 

 such a way as to bring the upper lobes ready to discharge the 

 pollen down on the back of 

 the insect. On visiting an- 

 other flower where the pistil 

 is older the insect on enter- 

 ing brushes some of the 

 pollen off on to the stigma. 

 The orchids show some of 

 the most remarkable move- 

 ments of any flowers during 

 cross-pollination. In some the pollen mass (pollinium) is 

 attached to a slender curved stalk which is held in tension 

 like a spring, and on the other end is a viscid disk. When the 

 insect alights on the labellum and touches a sensitive structure, 

 the pollinium is set free, the tension of the curved stalk causes 

 it to fly out like a spring, and the viscid disk attaches itself to 

 the head or to the proboscis of the insect. In this position it 

 stands pointing upward, holding the pollinium too high to touch 

 the stigmatic surface of that flower. In the course of half a 



minute or a minute, the stalk 

 curves downward in such a 

 position that the pollinium 

 will strike the stigmatic sur- 

 face. But by this time the 

 insect has gone to another 

 flower and cross-pollination 

 is effected.* In some mem- 

 bers of the pea family (plants like Cytisus, Spartium, etc., grown 

 in greenhouses are excellent to experiment with) the pistils and 

 s.amens are held in the keel. When an insect alights on the 



* Darwin's work "On the Fertilization of Orchids by Insects" should be 

 consulted. Full descriptions and illustrations are given. 



13 



Fig. 146. 

 Flower and stamens of common sage. 



