LEGUMINOSAE 



263 



present that despite the absence of nectar, and the whip-like action of the style, 

 the bee continues to visit other flowers. 



While the honey-bee is obliged to make considerable efforts before it can effect 

 explosion, the stronger and heavier humble-bees (Bombus terrester and B. lapidarius) 

 do this with the greatest ease. 



Cross-pollination takes place because the style springs out of the carina a 

 moment sooner than the stamens, so that the stigma of the second flower visited 

 is dusted with foreign pollen. Even the first flower visited will very probably be 

 crossed, though its own pollen lies all around, for the style rolls up to such an 

 extent that the stigma once more faces upwards, so that subsequent visitors may 

 still effect cross-pollination. The honey-bee and humble-bees hardly ever settle on 

 exploded flowers, which are almost exclusively visited by smaller bees, hover-flies, 

 or flower-beetles. Failing visits from humble-bees or the honey-bee, explosion does 

 not take place. Darwin states that in this case the flowers remain unfertilized. 



FlG. 82. Sarothamvus scoparius, Koch (after Herm. Muller). (1) Flower seen from the side. 



(2) The same with vexillum somewhat more erect, to show the nectar-guides ; seen from the right front. 



(3) The same after removal of the vexillum, seen from above. (4) The same, after removal of the alae. 

 (4 b) The left ala, seen from the inner side, showing the fold_/J which lies upon a projection (4 c and 6f) of 

 the carina. (4 c) The projection of the carina, seen from the front. (5) Position of the stamens and 

 pistil in the unexploded flower. (6) Flower after explosion of the short stamens and removal of the 

 vexillum and alae ; seen from the side. (7) Position of the parts after explosion. (8) Staminal tube, split 

 longitudinally to the right of the posterior stamen (1) and spread out. (9) End of the style with the 

 stigma () seen from the inner side ; pi, the plate which scatters the pollen. 



Visitors. Only strong eutropous bees with a long proboscis (Apis, Bombus, 

 Eucera) are able to set the flower mechanism in motion. Other bees (mostly 

 hemitropous), po-dvg. hover-flies, and po-dvg. beetles, can only, as already stated, 

 plunder flowers that have already exploded. 



Hermann Muller (H. M.) in Westphalia, Loew (L.) in Brandenburg, Alfken (A.) 

 in Bremen, Verhoeff (V.) in Norderney, and myself (Kn.) in Schleswig-Holstein 

 have observed the following bees, all po-dvg., as legitimate visitors. 



