Dear Sir,

I am truly sorry to have allowed your two kind letters to remain so long unacknowledged. The first came (with the Tables returned), when I was with a yachting party north of Scotland, & the second when I was much occupied after my return home.¹ I have since waited to say something of our further observations about Fairy-rings.² Late in the Autumn M^r. Lawes found on igniting some soil apparently covered with mycelium that it remained white after ignition.³ Following this up in the Laboratory we found that much at any rate of the white matter was incombustible; and qualitative chemical examination of the residue showed it to contain much carbonate of lime, and only traces of phosphoric acid, whilst the examination of the ash of some fungi (a. nudus) showed much phosphoric acid, and much potass, but scarcely traces of lime, thus confirming previous analyses of the ash of various fungi.⁴ It would thus appear that the white matter coating the soil at that date was exhausted mycelium? This is obviously an interesting point, and calls for further experiment at other periods of the year.

With regard to the fungi not reappearing where they have grown before in the case of fairy rings, may it not be a question how far this may be due to the exhaustion of the materials for growth by the fungi themselves or how far by the luxuriant growth of the grasses which succeed them—adding perhaps the force of competition to exhaustion? On this point I may mention that a friend assures me that in the case of a “ring” yielding edible fungi which are always gathered (and so do not manure the grasses)⁵ the crop reappears on the same and not on an annually extending ring. I may add that this autumn large specimens of Agaricus arvensis appeared in more or less complete rings on one of our highly manured plots where individual specimens had previously been observed.⁶ Otherwise the prominent development of rings is, as stated in the “Note,” on the plots exhausted of potass and of nitrogen in such condition as to be available to the other plants. There is obviously much left to learn before we know all about this curious subject; & I am extremely glad to hear that you are making observations upon it.

Pray accept my best thanks, better late than never, for your kind offer to send me a copy of your book on “Insectivorous plants”.⁷ I need hardly say I shall be proud to receive one from you. I was much interested to hear some notices of your observations on the subject given by Professor Dyer at meetings of the Scientific Committee of the Hort. Soc.;⁸ and I remember the question occurred to me at the time, whether the plants appropriated the animal matter directly, or only its products of decomposition. I am not aware of your evidence and arguments on this point; but the interesting facts you were good enough to communicate in your last letter, as to the remarkable rapidity with which phosphate & carbonate of ammonia are absorbed and affect the contents of the cells, are at any rate consistent with the supposition that it is the products of decomposition rather than the animal matters as such that serve as food to the plants?

I was much gratified, as also was my brother, the Editor of the Memoir, to hear that you had been interested in the Memorials of our dear Mother.⁹

With the best wishes of the season, | I am, Dear Sir | Your’s sincerely | J. H. Gilbert

Charles Darwin Esq^re., &^c. &^c. &^c.