II PRIMULACE^ 269 



similar, that of the long-styled being considerably 

 smaller than the other — X(jW of an inch in diameter 

 against \%'^^, or nearly in the proportion of three to 

 two — a difference the importance of which is probably 

 due to the fact that each grain has to give rise to a 

 tube which penetrates the M^hole length of the style, 

 from the stigma to the base of the flower ; and the tube 

 which penetrates the long-styled pistil must therefore 

 be nearly twice as long as in the other. Darwin 

 showed that much more seed is set if pollen from the 

 one form be placed on the pistil of the other than if the 

 flower be fertilised by pollen of the same form, even 

 when taken from a difl'erent plant. Nay, what is most 

 remarkable, such unions in Primula are more sterile 

 than crosses between some nearly allied though dis- 

 tinct species of plants. Darwin's explanation has 

 been generally accepted by botanists. It has, how- 

 ever, been questioned by the late Mr. E. Bell in a 

 special work (The Primrose and Darwinism, by a 

 Field Naturalist), and again in a paper " On the 

 Pollination of the Primrose," in Nature Notes for 

 April. This paper has a pathetic interest, as the 

 author, who had been for some time in bad health, 

 died before it was published. Mr. Bell scarcely appre- 

 ciated, I think, the cases of insect visits which are on 

 record, and the fact that while Darwin attributed the 

 fertilisation to night-flying moths, most of the obser- 

 vations have been made by day. The length of the 

 pistil varies very much both in the Cowslip and the 

 Primrose, and both sometimes produce equal -styled 

 varieties. 



P. veris (Cowslip) is visited by humble bees and 

 solitary bees in the day, and by moths at night. 



P. vulgaris (Primrose) is rarely visited by the larger 

 humble bees, and not often by the smaller ones. It 

 appears to be mainly fertilised by moths, but is some- 

 times visited by Bombus hortorum,. 



P. farinosa. — In the Alps this species is visited 

 principally by butterflies ; in lower districts by humble 



