# From Hubert Airy 2 May 1876

(I write from Norwich, but hope by the week’s end to be at)

Edensor. Kidbrook Grove. | Blackheath S.E.

2 May 1876.

(I write from Norwich, but hope by the week’s end to be at)

My dear Sir

When last I wrote to you, I think I mentioned that I was preparing a
fresh paper for the Royal Society, on a point of Leaf-Arrangement.^{1} It is now ready, and I shall be very much
obliged if you will give me permission to send it as communicated by
you.^{2} I think it has some features which you
would approve of. It consists of a description of the leaf-arrangement
of the Crowberry plant (Empetrum nigrum), with
some discussion of its bearing on the question of the significance of
leaf-ranks generally. Crowberry twigs are wonderfully fertile in
variations: Scarcely a twig did I find that did not present one or two
transitions from simpler to more complex orders in rising from base to
summit; but the curious point is that the transition 〈w〉as almost always
from an order of one phyllotac〈tical〉 series^{3}
(say the primary series, $\frac{1}{2}$, $\frac{1}{3}$, ^{〈 〉5}, ^{〈 〉/8} &c to an order of
another series (Say 〈the se〉condary series, $\frac{1}{4}$, $\frac{2}{7}$, $\frac{3}{11}$ &c.). Such transition could not be effected by any
process of uniform condensation,^{4} and I was
curious to learn exactly how it did take place, so I made an instrument
which enabled me rapidly to prick off on paper the arrangement of any
specimen: then I took fifty twigs at random, and pricked them off, and
made a careful comparison of the phenomena they presented. The result
delighted me. Forty six out of the fifty showed transition from an order
of one series to an order of another series,** and wherever the details
were traceable (for sometimes the change could not be traced when it
took place in the crowd of microscopic scales at the base of a fresh
year’s growth,) the transition was found to be effected by a curious
irregularity which I can only describe (without a diagram) as a spiral
dislocation between two adjacent spirals of
some secondary set. The result of such dislocation is a complete
derangement of all ranks not belonging to that set, and a creation of
new sets of ranks (with different numbers) in th〈eir〉 stead, thus
producing a wholly new arr〈angemen〉t to go on with.

**Such as the following:—

Transition | from | $\frac{2}{5}$ | or | $\frac{3}{8}$ | to | $\frac{2}{7}$ | in | 22 | instances. |

— | — | $\frac{2}{5}$ | or | $\frac{3}{8}$ | to | $\frac{2}{9}$ | — | 5 | — |

— | — | $\frac{2}{5}$ | or | $\frac{3}{8}$ | to | 5-whorls | 1 | — | |

— | — | 3-whorls | to | $\frac{2}{7}$ | — | 2 | |||

— | — | $\frac{2}{7}$ | to | 4-whorls | — | 10 | |||

— | — | $\frac{2}{7}$ | to | α^{†} |
— | 2 | |||

— | — | $\frac{2}{7}$ | to | $\frac{2}{9}$ | — | 〈 〉 | |||

— | — | 4-whorls | to | $\frac{2}{9}$ | — | 〈 〉 | |||

— | — | α^{†} |
to | $\frac{2}{11}$ | — | 〈 〉 | |||

— | — | $\frac{2}{9}$ | to | 5-whorls | — | 〈 〉 | |||

— | — | $\frac{2}{9}$ | to | $\frac{2}{11}$ | — | 1 | |||

— | — | 5-whorls | to | $\frac{2}{11}$ | — | 1 | |||

Total 64 in fifty twigs. |

(+ *Ga is a 4-6-10-ranked order, such as may be found in scabious-heads.)

This fact suggests remarks on the undue prominence given in some
botanical text-books to the ‘primary’ or ‘generating’ spiral,^{5} which in Empetrum n.
is seen to have no more enduring value than any other geometrical rank,
but is broken up 〈at〉 each transition, while a new one arises turning in
the opposite direction.

The only description I have met with of anything like these changes of
leaf-order, is in the Rev^{d}.
G. Henslow’s paper (Trans. Linn. Soc. vol. XXVI p. 647)
“On the Variations of the Angular Divergences of the Leaves of Helianthus tuberosus.”^{6}
The Variations in that plant appear to be similar in character to those
of Emp. n., but much more limited in
range; and M^{r}. Henslow appears to me to have
missed the meaning of the geometry of the case. Indeed, without
instrumental appliances it would be very difficult to make it clear.
Accordingly in my paper I venture some critical remarks upon M^{r}. Henslow’s.^{7}

Along with my paper I propose to send the original fifty pricked
diagrams, two of which I take as typical and refer to in describing
th〈e〉 details of transition; and at the end of the
〈 〉 I give a description of the ins〈trumen〉t
which 〈 〉d, and fondly name it “taxigraph,” and
express hope tha〈t i〉t will prove useful to other observers.— Perhaps
the instrument itself might as well be exhibited.^{8}

In the course of the paper I take the opportunity of standing up for my
theory of leaf-arrangement being determined by the geometrical
conditions (of relative position) imposed upon the nascent leaves by the
need of mutual accommodation under mutual pressure in the bud, which I
see more and more clearly to be the ruling principle of
leaf-(arr〉angement.^{9}

I think I have said enough to give you an idea of the scope of my paper,
and if you approve of it I hope you will not object to my using your
name as communicating it to the R.S.^{10}

Will you kindly remember me to your circle, and believe me | Yours very sincerely | Hubert Airy

Charles Darwin Esq. M.A. | Down, Beckenham. | Kent.

## Footnotes

*Correspondence*vol. 22, letter from Hubert Airy, 13 March 1874 and nn. 1 and 2).

*Correspondence*vol. 20, letter from Hubert Airy, [before 15] July 1872, and

*Correspondence*vol. 21, letter from Hubert Airy, 17 March 1873).

## Bibliography

Airy, Hubert. 1873. On leaf-arrangement. Abstract. Communicated by Charles Darwin. [Read 27 February 1873.] *Proceedings of the Royal Society of London* 21 (1872–3): 176–9.

Airy, Hubert. 1876. On the leaf-arrangement of the crowberry (*Empetrum nigrum*). Abstract. Communicated by Charles Darwin. [Received 8 May 1876.] *Proceedings of the Royal Society of London* 25 (1876–7): 158–60.

Bentley, Robert. 1861. *A manual of botany: including the structure, functions, classification, properties, and uses of plants.* London: John Churchill.

*Correspondence*: *The correspondence of Charles Darwin.* Edited by Frederick Burkhardt *et al.* 27 vols to date. Cambridge: Cambridge University Press. 1985–.

## Summary

On his new paper for Royal Society on a point of leaf arrangement. Asks CD to communicate it and "gives some details of its contents", e.g., recorded observations of changing leaf-order on individual specimens.

Comments on a paper by George Henslow ["*Helianthus
tuberosus*", *Trans. Linn. Soc. Lond.* 26 (1876):
647].

## Letter details

- Letter no.
- DCP-LETT-10490
- From
- Hubert Airy
- To
- Charles Robert Darwin
- Sent from
- Blackheath
- Source of text
- DAR 159: 30
- Physical description
- 4pp damaged

## Please cite as

Darwin Correspondence Project, “Letter no. 10490,” accessed on 4 March 2021, https://www.darwinproject.ac.uk/letter/DCP-LETT-10490.xml

Also published in *The Correspondence of Charles Darwin*, vol. 24