LEGUMINOSAE 



289 



states that the nectar is concealed in the base of a tube 9-10 mm. long, formed bv 

 fusion of the nine lower filaments with the claws of the petals. The upper free stamen 

 lies on one side of the flower, so that the whole of the cleft in the staminal tube 

 serves as a nectar passage. When a bee thrusts its proboscis under the vexillum 

 towards the nectar, it holds on with its fore-legs to the alae, which are united with 

 the carina, while its other two pairs of legs are supported by deeper parts of the 

 capitulum. The pressure exerted depresses the carina and alae, so that the stigma 

 protrudes, to be immediately followed by the upwardly dehisced anthers, which press 

 against the under-side of the bee's head. The stigma consequently receives pollen 

 brought from another flower, and this is replaced by a fresh supply. Cross-pollina- 

 tion is thus assured. Self-pollination may also take place when the head of the bee 

 is withdrawn, but Darwin says 

 that this is ineffective (though 

 Kerner is of the opposite opinion), 

 and is rendered inoperative by 

 the previously effected cross- 

 pollination. 



The return of the parts to 

 their original position, after re- 

 moval of the pressure exerted by 

 the insect, is brought about by 

 the intrinsic elasticity of the base 

 of the carina. The thin easily 

 rotated claws of the alae separate 

 from the common tube, and the 

 two large vesicular processes of 

 these petals grasp the reproductive 

 column from above, their elasticity 

 keeping the stamens, pistil, and 

 the parts which enclose them, 

 in their proper positions. The 

 staminal tube is continued into 

 free, stiff, upwardly curved fila- 

 ments, somewhat thickened at the 

 end ; the style curves upwards 

 between them in such a way that 

 the stigma projects above the 

 anthers to some extent. 



In order to reach the nectar legitimately, an insect must have a proboscis of 

 at least 9-10 mm. in length, corresponding to that of the corolla-tube. Many 

 species of humble-bee and other bees are regular pollinators, and some Lepidoptera 

 are casual agents of cross-pollination. The pollen, on the other hand, is accessible 

 to all short-tongued insects which are skilful enough to depress the carina. Such 

 insects, e.g. the honey-bee, also effect regular cross-pollination. Nectar is also 

 stolen from the red clover, especially by Bombus terrester (with a proboscis only 

 7-9 mm. long), and the honey-bee (with a proboscis of 6 mm.); these perforate 



Fig. 93. Trifolium praUnse, L. (after Herm. Miiller). 

 (l) Flower seen from below. (2) The same, after removal of 

 the vexillum ; seen from above. (3) Anterior part of the same 

 with the edges of the carina pressed apart (enlarged to twice the 

 scale of I and 2). (4) Right ala, with the claw torn off; seen 

 from the inner side. (5) Right half of the carina, with the claw 

 torn away ; seen from the outside. (6) The depressed carina, 

 with the protruding anthers and stigma (at a higher level); seen 

 from the side, a, calyx ; 5, tube formed by fusion of 9 6laments 

 with the claws of the petals; c, vexiltum ; d, hollow on the inner 

 side of the ala ; «, lower border of ala ; f^ outside of ala ; g^ base 

 of ala dilated into a vesicular process ; h^ carina ; i', style ; ife, free 

 upper stamen ; /, stigma ; »«, anthers ; w, point of fusion between 

 alae and carina ; (3, point at which the carina is moved up and 

 down ; p, outwardly curved part of the upper margin of the ala ; 

 q^ expansion of the vexillum, folded over below. 



