MELANISM AND MELANOCHROISM. 
79 
tends to produce a large, pale variety ; while small, dark 
specimens result from dry and stunted food. (2). Resinous, and 
other strong vegetable properties, produce distinct brown 
markings. (3). Chalk soils produce a chalky white or bright 
colour in insects : conversely we should expect rich loamy 
soils to be haunted by deeply-coloured moths. (4). A cold 
climate, or the gloom of damp dark woods, causes a bleached 
appearance and general absence of distinct markings.” 
These conclusions are all more or less open to very serious 
objection. In No. i, it has never been proven in the slightest 
degree that succulent food produces pale, and dry and stunted 
food produces dark varieties, other than in the direction I 
have previously pointed out with regard to the relation that 
colour bears to comparative size. This is assumed practically 
by Mr. Robinson who associates “ large ” with “ pale ” and 
“ small ” with “ dark.” Nos. 2 and 3, I consider a simple 
outcome of the most elementary law of “ natural selection,” 
for the dark brown colour of fir-feeding species is of the 
utmost necessity for protection, when such species are resting 
on the dark fir-trunk, e.g., Boannia abietaria, Ketinia resinana, 
Thera variata^ and many others ; and the cause of the 
occurrence of pallid species and varieties on chalk needs no 
further discussion. That part of No. 4 referring to cold has 
already been dealt with, and “ bleaching and general absence 
of distinct markings ” has been proven to accompany a cold 
climate, but the part referring to “the gloom of damp dark 
woods” is purely theoretical and unsupported by fact, vide 
what has been previously written concerning the Huddersfield 
and Derby melanic varieties. 
Still continuing the discussion relative to food as a cause, 
Mr. Cooke {Entom. x., p. 152) writes : — “ The extraordinary 
dark varieties in Scotland cannot have been caused by smoke 
or chemicals, but they are, as far as my experience goes, 
produced' in black bog or peat soil, which, I suppose, contains 
a large amount of carbon ; and this may have the same effect 
on the caterpillars, through the tissues of the foodplants con- 
taining more carbon than in other situations, as when the 
caterpillars eat the carbon in the form of soot along with their 
food ; and again, although the country immediately around 
York is purely agricultural, yet I am satisfied there is a 
sufficient amount of soot deposited on the plants to affect the 
colours of the Lepidoptera.” Here again the actual fact of 
the dark varieties being produced “ in black bog or peat soil ” 
