66 



natural selection and heredity, we would arrive at a common 

 result. 



Many observers have been at work, and much careful 

 thought has been devoted to the subject, as shown in Mr. 

 Tutt's 'Melanism and Melanochroism,' published in 1891, 

 where smoke and moisture, the latter more especially in 

 association with woods, are considered as the determining 

 factors in producing melanism. 



Before accepting a general hypothesis such as this it is 

 advisable to test it by considering how it fits in with the 

 facts in reference to various individual species. Now, it 

 appears to me that when considered in connection with such 

 a species as A . nebulosa, the contradictions are too great to be 

 ignored. 



Mr. E. J. Burgess Sopp, F.R.Met.S., has been good 

 enough to send me statistics of the rainfall and humidity of 

 various parts of the country. Taking a period of ten years, 

 I find that the New Forest has more rainfall than the 

 Delamere District, but about the same mean humidity, 

 North Cornwall has a decidedly heavier rainfall and rather 

 more humidity, while the London district has less rainfall 

 and humidity. I have not got the figures for Argyleshire. 



Briefly A. nebulosa is pale in the New Forest and in 

 Cornwall, where we have moisture associated with woods. 

 Again, in Argyleshire, where we certainly have a moist 

 climate, so far as I know, only a light form occurs, very 

 similar to the Cornish. Then in Ireland, where many 

 species are melanic, I have never heard of dark A . nebulosa, 

 but I must admit my knowledge of the Irish forms is meagre. 



In Epping Forest, where smoke comes into play, we get a 

 darker grey, but nothing approaching a black form. 



In Delamere Forest, where there is more rainfall than in 

 Epping Forest, but less than in Cornwall and the New 

 Forest, and where smoke has not played a part, we do get 

 extreme melanic forms. 



With regard to Delamere Mr. Mansbridge writes me : 

 " I am quite unable to regard this as a smoke-affected area. 

 Its geographical position in relation to the positions of the 

 manufacturing centres of S. Lancashire and Cheshire quite 

 precludes this. I do not think that resting surfaces are at 

 all darker than in southern woods of the same character — e.g. 

 St. Leonards and Tilgate Forests, Sussex." Mr. Harrison, 

 who knows Delamere Forest well, fully concurs in these 

 remarks : 



" I do not think that melanism as instanced by A. nebu- 



