My dear Sir

I am ashamed to have kept the books and papers you lent me, for such a length of time, and I fear my delay may have inconvenienced you—¹ I have only just done with them, for I found so much to study and take notes of, esp^ly. in the tough Teuton tongue, that the perusal took much longer time than I expected— Moreover I have had but little spare time lately, and am likely to have still less in the future, for I have recently been appointed a medical inspector under the Local Gov^t.² Board, which is a capital thing in itself but unfavourable to the study of Phyllotaxy. I don’t know when I shall be able to write and publish what I have to say.³

De Candolle has done well in demonstrating geometrically the numerical relations between leaves that successively approximate to the vertical through one taken as start^g. point, when certain conditions are granted, but his general conclusions rest on a very partial and imperfect survey of the facts of leaf-arrangement, ignoring any distinction between leaf-orders so different as those of elm and Scotch fir. (not that he mentions those or any others, but that is the upshot of his argument.)⁴

Kerner’s Alpine studies are delightful— How beautifully he accounts for the rarity of Alpine Annuals! I say Amen to his “Vorwort.”⁵

Braun’s “Rejuvenescence” gave me great pleasure. I was so glad to meet with a good discussion of vine growth.⁶

But it made my heart beat when I saw Fig. 144 in Sachs’ “Lehrbuch der Botanik,” and still more when I read “Auf den ersten Blick erscheinen solche Stellungsverhältnisse wie zweizeilige, die durch Drehung des Stammes verändert worden sind,”—my own idea, exactly, and I cannot conceive how he could leave hold of it, as he does in the next words—“was in diesem Falle kaum annehmbar scheint.”

I have taken the liberty to mark the relevant passages in Sachs, in case you might care to look at them—⁷ —But that figure 144 is worth a Jew’s eye:⁸ some of my diagrams of ivy are exactly like it; and it would fairly represent the leaf order in a lateral twig of Sp. Chestnut or Portugal laurel.

Among your own MS. notes, which you were so kind as to trust to my care, I found some words which interested me very much as showing that you yourself were disposed to regard the relative positions of leaves as determined by conditions of mutual pressure. The fragment is dated June 11,/63, concerning Euphorbia amygdaloides, and the words (if I read them aright) are these:—“Now I can no more believe there is special law than for marbles shaking together, standing in intervals on others so as to pack closest.”⁹

My own ‘marble’ experiments have had rest of late, but I hope to carry them out some day, though I do not regard them as of primary importance— I think the oak galls suffice for ocular demonstration.¹⁰

I wish, if I have time, to offer an essay on this subject to the Royal Society, though I fear my views are too crude, and I do not see how I can devote time and study enough to bring them to maturity.¹¹

Your books are packed, and shall be sent by rail to Orpington tomorrow— Accept my best thanks for your kindness in lending them to me, and believe me with kind regards to M^rs. Darwin and your family, | Yours very sincerely | Hubert Airy

Cha^s. Darwin Esq^re. MA., FRS.