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CHAPTER XVI. 
OF COLOUR, 
There is no subject connected with the vital phenomena of 
either plants or animals more unintelligible than the distri- 
bution of colour over their surface; a distribution which is 
evidently caused by some fixed rule, because we often see it 
perpetuated, with little or no variation, from generation to 
generation, but concerning the primary cause of which we 
are as much in the dark as ever. 
In De Candolle’s Physiologic Vegetale there is a good 
account of what was known or conjectured upon this subject 
in the year 1831, particularly of the views of Schiibler and 
Funk; since that period the subject has been investigated 
by several persons, especially by Mohl, whose views are 
incorporated in the following sketch. 
Every one must have been struck with the singular, and 
often complicated, manner in which the various and varying 
colours of organic matter are arranged. We see in birds the 
plumage marked with contrasts of the most dissimilar colours, 
reproduced with an exactness which is wonderful; we find 
the breeders of curious races of animals able to preserve 
peculiar kinds of marking, and even to improve them, with 
admirable precision ; we also know that in plants, without any 
visible constitutional change, without accident, and without 
any known predisposing cause, a yellow flower will become 
pink, and a pink one yellow ; and we see that, if the portion 
of a stem thus altered be increased by the division of itself, 
the change is fixed and may be multiplied for ever. A dingy 
brownish purple tulip will suddenly, and without warning, 
burst forth in radiant beauty, its dull colour dispersed, a pure 
and spotless white taking its place in part, and the brightest 
and deepest streaks of crimson adding richness to its purity. 
If we look minutely to these circumstances, we shall find that 
