LEGUMINOS^ 



149 



and the pistil springing out of the keel elastically. 

 Such blossoms permit only one useful visit. 



(a) Honey-containing flowers : Medicago. 



(6) Honeyless flowers. 



(a) The bee touches the pollen and the stigma 

 with its under side : Genista, Ulex. 



{l3) The bee is powdered with pollen and stigma 

 on the back : Sarothamnus (Broom). 



3. Piston mechanism : those -in which the pressure 

 of the bee pumps out, as it were, a certain quantity of 

 pollen ; the flower resuming its original form when the 

 pressure is removed. The thickened filaments press the 

 pollen in single portions out of the top of the keel. 

 Frequent insect visits are necessary for its fertilisation. 



(a) Honey -containing flowers : Lotus, Anthyllis, 

 Tetragonolobus, Hippocrepis. 



(6) Honeyless flowers : Ononis, Lupinus, Coronilla. 



4. The brushing arrangement : that in which, on 

 the pressure of the bee, the 

 pollen is swept out by a brush 

 of hairs situated on the end 

 of the pistil. This case does 

 not seem to differ much from 

 the preceding. 



{a) The top of the pistil 

 is straight : Lathyrus, Pisum, 

 Vicia, Lens, Robinia. 



(b) The top of the pistil is 

 twisted in the form of a snail : 

 Phaseolus. 



The power of self-fertilisa- 

 tion seems to be lost in some 

 species of Phaseolus, Onobry- 

 chis, and Sarothamnus ; and 

 to be much diminished in 

 others, as in Trifolium repens 

 and Vicia Faha. 



Some species throw their 

 seeds, owing to the elasticity of the pods, which. 



Fig. 88, 



1, Pod of Comnioii Vetch. 

 The line ab shows the direction 

 of the woody fibres. 2, Pod of 

 Common Vetcli after bursting 

 open. 



