30 ON ELOWERS AND INSECTS. [LECT. 



during the day by humble bees, this is not the case with 



the Primrose, which, in Mr. Darwin's opinion, is fertilized 



almost exclusively by moths. 



The genus Ly thrum (Fig. 33) affords a still more 



complex case, for here we have three sets of flowers. 

 The stamens are in two groups ; 

 in some plants, the pistil projects 

 beyond them ; in the second form 

 it is shorter than any of the sta- 

 mens, and in the third it is in- 

 termediate in length, so that the 

 stigma lies between the two sets 

 of anthers. These three positions 

 appear to correspond respectively 

 to the head, thorax, and abdomen 

 of the bee. 



Although flowers present us 

 with these beautiful and complex 



FIG. 33.Lythrum salicaria. 



contrivances, whereby the transfer 



of pollen from flower to flower is provided for, and 

 waste is prevented, yet they appear to be imperfect, 

 or at least not yet perfect in their adaptations. Many 

 small insects obtain access to flowers and rob them 

 of their contents. Malva rotundifolia can be, and 

 often is, sucked by bees from the outside, in which 

 case the flower derives no advantage from the visit 

 of the insect. In Medicago sativa, also, insects can 

 suck the honey without effecting fertilization, and the 

 same flower continues to secrete honey after fertiliza- 

 tion has taken place, and when, apparently, it can 

 no longer be of any use. Fritz Miiller has observed 

 that, though Posoqueria fragrans is exclusively fer- 



