ENTOMOPHILOUS FLOWERS 



127 



6. Bke-flowers. — These are regularly pollinated 

 by bees and wasps. Zygomorphic flowers predomi- 

 nate in this class, and the predominating colours are 

 red, blue, and violet. In the most highly specialized 

 types of this class, such as most Orchidacecs, only a 

 few species of bee can effect pollination. The struc- 

 ture of the flowers of Orchids, described in Chapter 

 XV, shows clearly that the pollinia cannot possibly 

 reach the stigma without the help of an external 

 agent. That agent 

 is a long-tongued 

 bee, which, attracted 

 by the gorgeously- 

 coloured labellum, 

 alights on it as on a 

 platform, and, find- 

 ing the opening (j/>) 

 to the nectar-holding 

 spur too narrow for 

 its entrance, sends 

 its long tongue into 

 the spur for the pur- 

 pose of sucking honey (fig. no). In this attempt its 

 forehead comes into contact with the rostellum (/-), 

 which is thus either pushed back or breaks, and the 

 pollinia {po) come out and stick to the bee's forehead by 

 means of the sticky disks and stand upright (i) on it. 

 By the time the bee visits the next flower, the upright 

 caudicle bends forward (2) and brings the pollinia in 

 such a position that they point towards and touch the 

 receptive stigma {sf) of the flower. Now the stigma, 

 with its viscid secretion, grasps the pollen-masses in 

 such a manner that either the whole pollen-mass or a 

 portion of it adheres to the stigma. This wonderful 

 mechanism of cross-pollination brings out prominently 



Fig. 1 10.— Flower of Orchis 



A Labellum. sf>. Opening into the spur. st. 

 Stigma, r, Rostellum. /o, Pollinia. 5, Sepal. 

 /, Petal. I. Pollinium as it first sticks to pencil 

 head, a, Same with caudicle bent later on. 



