i.] IMPERFECTION OF FLOWEES. 29 



between flowers of the same species which. Mr. Darwin 

 has proposed to call Dimorphism, is found in most 

 species of the genus Primula, but not in all. 



The Cowslip and Primrose resemble one another in 

 many respects, but the honey they secrete must be very 

 different, for while the Cowslip is habitually visited 

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

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

 tilised almost exclusively by moths. 



The genus Ly thrum 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 

 stamens, and in the third it is intermediate in length, so 

 that the stigma lies between the two sets of anthers. 



Although flowers present us with these beautiful and 

 complex 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 per- 

 fect in their adaptations. Many small insects obtain 

 access to flowers and rob them of their contents. Malva 

 TOlundifolia can be, and often is, sucked by bees from 

 the outside, in which case the flower derives no advan- 

 tage from the visit of the insect. In Medicago sativa, 

 also, insects can suck the honey without effecting fer- 

 tilisation, and the same flower continues to secrete honey 

 after fertilisation has taken place, and when, apparently, 

 it can no longer be of any use. Fritz Muller has 

 observed that, though Posoqueriafragrans is exclusively 

 fertilised by night-flying insects, many of the flowers 

 open in the day, and consequently remain sterile. It is 

 of course possible that these cases may be explained 



