From Hubert Airy   13 March 1874

My dear Sir

I have re-written my paper on Leaf-arrangement, embodying the views contained in my last two letters to you; and I propose to send it to the Royal Society, in spite of the unfavourable criticism which the former paper met with from the R.S. referees.¹

May I beg the favour of a line from you to say if you will be kind enough to “communicate” my new paper to the Society—?—though I am almost ashamed of asking you to stand godfather to something that may be doomed to suffocation.² If the R.S. decline to print it, I shall certainly get it published in some journal (probably Nature), for I am sure it has a grain or two of truth in it which may thrive on wider criticism. I think I have found a new principle which has played an important part in the history of leaf-arrangement,— I mean spontaneous variability in the number of vertical leaf-ranks.³

The variations which present themselves at the present day are such as (I believe) cannot be explained on any other hypothesis. Let me mention a single example— I have found three ash-shoots, all rising from the same stump, the first exhibiting perfect crucial order (whorls of 2, the normal leaf-order of ash), the second exhibiting perfect alternate ($\frac{2}{5}$) order, and the third exhibiting perfect whorls of 3.

I cannot see how any one of these three arrangements could have been modified by slow degrees into any other of the three; but if by a sheer stroke of variation the old stump produced buds with 5 and 6 vertical ranks as well as buds with 4, I can see that, while 4 ranks would almost necessarily be packed into crucial order, 5 would almost necessarily be packed into alternate order $\frac{2}{5}$, and 6 into whorled order with whorls of 3.— And I suppose there may have been similar strokes of favourable variation in former days.

On many of the forms so produced, I suppose vertical condensation to have operated.⁴

Can you tell me if there is variability in the number of rays of any species of Star-fish?— Different species, I believe, have different numbers of rays; and that difference of number could only have been produced (I suppose) by strokes of variation.⁵

If such be the case, it furnishes a striking analogy to what I suppose to take place in the vegetable kingdom.

An echinus and an echinocactus⁶ might fairly share alike in the operation of so general a cause as that (supposed) of variation of number of vertical (or radial) ranks.

The two points on which I am troubling you are

1. ? Communication of paper to R.S.

2. ? Variability of rays of star-fishes.

Believe me, my dear Sir, | Yours very sincerely, Hubert Airy

Charles Darwin Esq. M.A., F.R.S.