80 RECIPROCAL NUTRITIVE DISJUNCTIVE SYMBIOSIS 



cleistogamous flowers) which never open, are self-pollinated and 

 produce seed abundantly. 



The legume family contains a very large number of bee flowers, 

 several of which never produce seeds unless visited by bees. Many 

 members of this family have 9 of the 10 stamens united into a tube 

 and the nectar, if any is present, is at the bottom of the tube. Four 

 of the petals, the 2 forming the keel and the 2 wing petals, are inter- 



FiG. 30.— White clover {Trifolium repens), a bee flower. After pollination 

 the flowers all bend downward and turn reddish, then brown. (See Fig. 31.) 

 (From the Flower and the Bee, by John H. Lovell; copyright, 1918, by Charles 

 Scribner's Sons. By permission of author and publisher.) 



locked, around the stamen tube, while the fifth, called the standard 

 is broad and more or less erect. When a bee visits the flower for 

 nectar it rests on the wing petals, which act as levers, and, bracing 

 its head against the standard, depresses the keel enough so it can 

 reach the nectar with its mouth parts. While it is doing this pollen 

 is applied to the under side of its body. If the bee is not strong 



