Dear Sir,

I have to thank you very much for your kind comments upon my paper, and for the pains which you have taken in pointing out its weak points.² I am also greatly obliged to you for the numerous references which you give me, especially that to R. Sachsse’s Farbstoffe, which I have not yet heard of.³ I shall look up the various works and passages you mention, and alter the paper in the senses you indicate.

With regard to Mr. Nicholson’s statement that I had published an article on the analogies of plants and animals, there must be some mistake of name, I think.⁴ I have talked over the subject with Mr. Nicholson, and have always felt much interest in it—especially from the point of view of Energy—but I have certainly nothing original to offer on the question, and have never written upon it.

There are two points in your letter on which I should like, with due deference, to make a remark. The first is this:— I tried as much as possible to avoid the chemical statement of pigments, because obviously I know no more about the subject than can be gained by looking at plants as they grow: but when I wrote a first rough draft and only discriminated between energy-absorbing structures (green leaves or their equivalents) and energy-expending structures, (bulbs, seeds, flowers, growing shoots &c), classing the first as mainly green, the second as apt to assume bright colours other-than-green,—a chemical friend (the Aldrichian Demonstrator in this University)⁵ objected that the introduction of so ultimate a principle as Energy was needless;—and I accordingly changed it for the expression “oxidation-products.” I see, now, from what you say, that I should have done better to keep to my original phraseology. Briefly, my fundamental observation is this— Chlorophyll, as a whole, in spite of occasional exceptions, gives a green hue to structures in which it largely exists as an active agent: but wherever any upsetting of its ordinary functions occurs, and in all parts where matters other than active chlorophyll occur, there is a more or less pronounced tendency to other colours. No doubt, as you suggest, green may occur in such parts also: but still, I think there are grounds enough for the rough generalization in spite of this—viz. that energy-expending portions of plants show a tendency to bright hues. The generalization, so expressed, is, I think, independent of special chemical or physiological facts:— I mean, it can be verified by observation alone, without the aid of analytic experiment. The generalization may look unimportant in the world as we see it now: but if we place ourselves in imagination among the green acrogens and conifers, the spores and anemophilous flowers, of a carboniferous forest, does it not begin to have a great deal more value? If we think, not of the developed entomophilous flower, but of the steps by which it developed, does not the fact that bright colours are apt to occur where energy is being expended, become a key to the whole process of its evolution?⁶

The second point—a shorter one—is this. I did not mean to suggest that the colours of fruits or flowers had anything to do with the appearance of insects, birds, or mammals at different geological periods, but merely with the development of a colour-sense in these animals.⁷ Even in this limited statement, I should refer chiefly to insects (especially bees and butterflies): for I see certain reason for thinking that all vertebrates alike inherit a certain amount of colour-perception from their common ancestor, or, at any rate, that the fishes share it with the terrestrial vertebrates. (However, as I mean to treat this question fully in my book, a copy of which I hope you will do me the favour to accept, I will not now bore you with it.)⁸ At the same time, I think we may allow that the colours, scents, shapes, and other peculiarities of developed flowers have had much re-active influence in modifying the insect organism—as we see obviously in bees, in butterflies, and in many protective devices or bits of mimicry:—and especially in modifying those portions of the nervous system on which tastes and instincts (meaning thereby, organically-regulated habits) depend.

With renewed thanks for your kind criticisms—of which I shall gladly avail myself for my book—and with apologies for again trespassing on your valuable time, I am, | Yours very faithfully, | Grant Allen.

P.S. It strikes me that Mr. Nicholson’s mistake may be due to the following cause. A paper appeared in a late number of the Cornhill with a title somewhat such as “Can we separate Plants from Animals?” As I am in the habit of contributing quasi-scientific articles to the Cornhill, Mr. Nicholson may have thought the paper was mine—which is not the case.⁹