Ɛpsilon

From H. C. Sorby   28 December 1881

Broomfield | Sheffield

Dec 28/81

My dear Mr. Darwin

Judging from what you say there appears to be no red colouring matter present in the plant that could be turned blue by the neutralization of free acid.1 I therefore suspect that the change is analogous to one that often occurs in more or less alkaline solutions. In most cases that I examined I was of opinion that the production of the colouring matter was due to the oxidization by the air of one or other of the different kinds of tannic acid but I am quite prepared to believe that other substances have the same sort of property and feel almost certain that this is so in the case of many lichens.2 On the whole I venture to suggest that the plant contains something changed into the colouring matter when in a slightly alkaline solution. If you could send me a little of the fresh plant I could make it out more certainly

I left off studying the colouring matters of plants in order to work up all the material I had collected for my two addresses at the Geological Society on the structure of rocks and since then have been led into a whole lot of new work by living on my yacht nearly half the year.3 The first few years I was learning what to do. The last I have done a fair lot of scientific work. Along with Prof. Herdman my first paper will soon appear on a number of new British Ascidians.4 I have splendid opportunities for collecting and observing and in a while hope to do good service to science in this department. I should do more if my attention were not so much directed to a sort of compound of art and science—art illustrating science and science helping art—which however is I hope useful in another department of knowledge. If I can in any way assist you in connexion with marine work in the English Channel &c I shall be very pleased and if you could suggest anything that it would be desirable to examine I should be very much obliged. I am attending to nearly all departments of scientific work along with the best authorities in each branch.

Trusting that you are well and being always most glad to do any little thing I can to advance the great questions you have so constantly in hand; wishing you a happy new year | I remain | Yours very truly | H C. Sorby

1
CD’s letter to Sorby has not been found. The plant pigments associated with red are anthocyanins; their colour changes from red to blue in less acidic (neutral) solutions.
2
Anthocyanins in water typically lose colour, but tannic acid acts as a co-pigment with anthocyanins, stabilising colour. Lichens are symbiotic associations of fungi and algae; the anthocyanin in lichens is derived from the algal component, as there is no anthocyanin in fungi.
3
Sorby had observed plant pigments using a modified microspectroscope that he first developed to examine mineral specimens (ODNB). He made his presidential addresses to the Geological Society of London in 1879 and 1880; the first of these was on the structure and origin of limestones while the second focused on the structure and origin of non-calcareous rocks (Sorby 1879, Sorby 1880). He spent his summers on his yacht, the Glimpse, dredging and making observations of the estuaries of Suffolk and Essex.
4
Sorby published a paper, ‘On the ascidians collected on the cruise of the yacht “Glimpse”’, co-written with William Abbott Herdman, in the Journal of the Linnean Society (Zoology), September 1882 (Sorby and Herdman 1882).

Please cite as “DCP-LETT-13585,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-13585