LEGUMINOSAE 



285 



' Bliitenbiol. Beob. in Thuringen,' ' Bliitenbiol. Beob. a. d. Ins. Riigen,' &c.) The 

 white or reddish flowers of this species smell like honey. The nectar is secreted 

 as usual, i. e. on the inner side of the base of the staminal tube. The calyx-tube 

 is only 3 mm. long, so that even short-tongued bees are able to reach the nectar. 

 Hermann Mtiller states that the alae are partly fused with the carina on either 

 side, so that both move simultaneously upwards and downwards. Their depression 

 by the weight of a nectar-seeking insect is facilitated by the fact that the claws 

 are very slender. These claws are fused for the most part with the staminal tube, 

 which is cleft above. The return of the parts to their original position is chiefly 

 due to the action of the vexillum and alae. The broad claw of the former grasps 

 the other petals, as well as the stamens and pistil, and, owing to its elasticity, 

 guides their bases back to the original position when the pressure is removed. 

 The front parts of the petals, and the reproductive column, return to their places 

 because the dorso-basal processes of the alae are converted into two elastic swellings 

 lying close together above the staminal tube. 



In order to reach the nectar, 

 an insect visitor must thrust its 

 head beneath the vexillum, and 

 in doing so has only the alae 

 for a support. These and the 

 carina are consequently pressed 

 downwards, and the vexillum 

 upwards, while stamens and 

 stigma protrude from the carina. 

 As the stigma projects some- 

 what beyond the anthers, cross- 

 pollination is greatly favoured. 

 Bees alone are able to work 

 the flower mechanism properly, 

 so as regularly to effect cross- 

 pollination; other visitors, e.g. 

 Diptera and Lepidoptera, only 

 do this occasionally. 



MacLeod gives a detailed 

 account of the flower mechan- 

 ism, which deviates in some 



respects from Miiller's description. He arrives at the following conclusions (Bot. 

 Jaarb. Dodonaea, Ghent, vi, 1894, pp. 342-9). 



The flower of T. repens consists of two co-operating (synergic) parts, i. e. the 

 alae and carina, which are united together, and move simultaneously in the same 

 direction. Each of these parts, however, may execute independent movements. 

 In this connexion two other organs have to be considered, the filaments (which 

 are passive) and the claw of the vexillum (which seems to play an active part). When 

 the alae and the carina of an unvisited flower are pressed down from 30 to 40 times 

 in succession, the mechanism does not appear to be exhausted: the reproductive 

 organs always return into the carina after the pressure has been removed. If, 



Fig. 92. Trifolium repens, L. (after Henn. Miiller). (i) 

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

 and vexillum ; seen from above. (3) Right ala, seen from the 

 inner side, a, nectar-passage ; c (?, pits in the carinal petals, into 

 which the alar processes fit; f, stigma; v v, dorso-basal alar 

 processes. 



