LEGUMINOSAE 



339 



234. Phaseolus L. 



Nectar-yielding bee-flowers with a stylar brush. The spirally twisted end 

 !)f the style, with the stigma and the pollen adhering to the brush, projects from 

 he tip of the carina (which is also spirally twisted) when this is depressed, return- 

 Tig again when the pressure is removed. Delpino (' Ult. oss.,' p. 55) says that 

 n some species the style is twisted to the right, in others to the left, and that all 

 ntermediate stages exist between a simple falciform curve (P. angulosus, &c.) and 

 1 helicoid spiral of 4 to 5 turns (P. Caracalla). 



809. P. vulgaris L. (Herm. Muller, 'Fertilization,' pp. 216-17; Kirchner, 

 Flora v. Stuttgart,' pp. 515-16; Knuth, ' Bloemenbiol. Bijdragen.') The flower 

 nechanism of this species was first described by Darwin (Gard. Chron., London, 

 857, p. 725, 1858, pp. 824-44, Ann. Mag. Nat. Hist., London, Ser. 3, ii, 1858, 

 >P- 459~64)- He also demonstrated by experiment that insect-visits are necessary 



Fig. 109. Phaseolus vulgaris \ L. (i) Flower seen obliquely from the front (from nature). (2) Pistil 

 enlarged (after Herm. Muller). e, ovary ; f, style ; g, stylar brush ; /;, stigma. 



)r fertilization. The bean, however, is able to fertilize itself with complete effect, 

 'arwin's account is here substantially repeated. The left ala is larger than the right, 

 'he base of the alar lamina is contracted, and bears an oblique tooth-like process, 

 rm and succulent, which fits into a carinal pit. On the lower third of the ala, 

 iternally, there is a crescentic fold, adapted to a corresponding groove in the carina, 

 'he latter is small, and the opening at its tip faces downward, lying above the tooth- 

 ke process of the right ala. The end of the style is somewhat expanded, and the 

 ijiique stigmatic surface is beset with a dense fringe of short hairs. This not only 

 revents the proboscis of an insect while being withdrawn from coming into contact 

 i.h the stigma of the same flower, but also prevents the escape of the stigmatic 

 aid, which is abundantly secreted by the stigmatic papillae when torn by contact 

 ith the rough bodies of insects. 



The anthers surround the style and shed their pollen upon it, but the stigma is 



'ver dusted. The upper free filament broadens out so much immediately in front 



the two nectar-passages that it grasps the edges of the staminal tube, completely 



osing it. There is here an oblique scale-like appendage directed upwards and 



