438 MR. C. DA-RWI"N ON SPECIFIC DIFFEBENCES IN PRIMULA. 



serve notice. As both species are dimorphic, their complete ferti- 

 lization depends on insects. They emit a different odour. The 

 Cowslip is habitually visited during the day by bumblebees (viz. 



Bomhus muscorum and hortorum, and perhaps by other species) and 

 at night by moths, as I have seen with the OuculUa. The Primrose 

 is never visited (and I speak after many years' observation) by the 

 larger bumblebees, and only rarely by smaller kinds; hence 

 its fertilization depends almost exclusively on moths. Conse- 

 quently the nectar in these two plants must differ much ; for 

 there is nothing in the structure of the flowers which can deter- 

 mine the visits of different insects. The utmost difference in the 

 colour of the corolla does not in tlie least prevent, as I have often 

 observed, a bee from recognizing the varieties of any species which 

 it may at the time be visiting. The Primrose, when legitimately 

 fertilized, produces on an average many more seeds than the Cows- 

 lip, namely, in aT)Out the proportion of 100 to 55. It is a more 

 important distinction that both the long-styled and short-styled 

 forms of the Primrose, when illegitimately fertilized with their own 

 pollen, are much more fertile than the corresponding forms of the 

 Cowslip when similarly treated. When long-styled plants of the 

 Cowslip are protected by a net, so that they cannot be visited by 

 insects, they yield no seed, as I found to be the case with no less 

 than eighteen plants ; and the short-styled form is only a little 

 less sterile. The long-styled Primrose, on the other hand, when 

 similarly protected, produces a considerable number of capsules, 

 of which twenty-three contained on an average 19*2 seeds: the 

 short-styled form produces under these circumstances fewer cap- 

 sules, of which fourteen contained on an average only 6*2 seeds. This 

 great difference in the fertility of the Cowslip and Primrose when all 

 insects which are capable of exclusion are excluded, depends in part 

 on the Primrose being innately much more self-fertile than the 

 Cowslip, and in part on the former being much frequented by 

 Thrips, which, dusted with pollen, may often be seen crawling 

 wathin the flowers. 



The Primrose, as everyone knows, flowers a little earlier in the 

 spring than the Cowslip, and inhabits slightly different stations and 

 districts. The Primrose generally grows on banks or in woods, 

 whilst the Cowslip is found in more open places. The geographi- 

 cal range of the tw^o forms is different. Dr. Bromfield remarks * 

 that " the primrose is absent from all the interior region of nor- 

 thern Europe, where the cowslip is indigenous.'^ In Norway, 



Pli} tologist, vol. iii. p. 094. 



