LEGUMINOSAE 



339 



234. Phaseolus L. 



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

 of the style, with the stigma and the pollen adhering to the brush, projects from 

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

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

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

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

 a 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 

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

 1857, P- 725, 1858, pp. 824-44, Ann. Mag. Nat. Hist., London, Ser. 3, ii, 1858, 

 pp. 459-64). He also demonstrated by experiment that insect-visits are necessary / 



Fig. lOf). PImsioliis vulgaris, L. (l) Flower seen obliquely from tlie front (from nalurel. (2) Pisiil 

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



for fertilization. The bean, however, is able to fertilize itself with complete effect- 

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

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

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

 internally, there is a crescentic fold, adapted to a corresi)onding groove in the carina. 

 The latter is small, and the opening at its lip faces downward, lying above the tooth- 

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

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

 prevents the proboscis of an insect while being withdrawn from coming into contact 

 with the stigma of the same flower, but also jirevents the escape of the stigmatic 

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

 with the rough bodies of insects. 



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

 never dusted. The upper free filament broadens out so much immediately in front 

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

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



