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Darwin Correspondence Project

From George Sigerson   8 July 1863

82 Talbot St | Dublin,

July 8. 1863

Dear Sir,

It occurs to me that there is one part of my paper which I did not make sufficiently clear.1 When it appeared in print I feared that my views were likely to be misunderstood through the faulty conciseness of my language. A specimen of orbicular leaf has been given, (Nelumbium speciosum) but I think that I should more fully have stated that it could by no means be supposed to realize the necessary condition of the orbicular.2 The round leaf of the Nelumbium I take to be merely a ‘segment’, the limb of which is modified in a peculiar way, and the plane of the limb also changed with respect to its petiole. The Orbicular leaf which is ideal, must of course be supported by its axis, and therefore be a plant of itself. The round leaf given is merely to make more easy to be understood the views I put forth. The disjecta membra of the orbicular type I had intended to investigate throughout the simpler forms of vegetable life.3 I was anxious to show, at once, that there is mutation in forms, and proved by actual facts that changes from comparatively simple to very complex forms do take place. Figures from 9 to 21 give examples which are evident proofs to any person, even though he be not a Botanist.4 It was to these facts that I wished to draw your attention, and receive your opinion upon them. I thought they would naturally interest you, having read with so much pleasure your views on the ‘Origin of Species’ &c.

With respect to the angle of divergence to which you are so kind as to draw my attention, it does not encourage me to undertake the investigation to say that you have failed. I confess that as yet I have been able to pay little attention to the subject.5 But, perhaps, you have remarked that I have perceived the angle to change for the leaflet coming off. (page 7, line 25, observations on change of direction in enlarging vein, in fig. 10, marked g.) It would be interesting to note the former angle, and the latter, comparing the difference with the progress of the leaflet in separating itself. This might give some clue. But, I do not wish to intrude crude speculations upon your attention.

At present, I am not in a position to pursue the subject, but I hope soon to be so; and, assuredly, the pleasure of acting upon your suggestion would equal to the pleasure of investigating an interesting point.

I have the honour to be, Dear Sir | Very truly Yours | Geo. Sigerson MD.

Footnotes

Sigerson 1863. No previous letters from Sigerson to CD have been found; however, there is a presentation copy of Sigerson 1863 in the Darwin Pamphlet Collection–CUL, the cover of which bears part of a May 1863 postmark.
In his paper, Sigerson sought to account for phyllotaxy in terms of modification from a ‘protomorphic leaf-type’, which he believed to be the ‘orbicular leaf’ (Sigerson 1863, p. 1). Sigerson stated that each orbicular leaf was borne at the end of an independently arising stem, and that the phenomenon of phyllotaxy would be explained by the modification of this prototype such that the several radial ribs of the orbicular leaf were arranged separately along the stem (that is, separated by internodes), each forming the mid-rib of a lateral leaf. He thought the leaves of Nelumbium speciosum presented a ‘good instance’ of the orbicular form (see Sigerson 1863, p. 1; see also plate 1, figure 1).
Disjecta membra: ‘scattered remains’ (OED). Sigerson stated in his paper that the ‘prototype’ of the orbicular leaf ‘must be sought in a still simpler form’, and that he believed it would be found ‘in a cell’ (Sigerson 1863, p. 1).
Figures 9 to 21 were designed to illustrate the transition from a simple to a compound leaf by gradual stages; most of them depicted leaves of the cultivated raspberry (see Sigerson 1863, p. 6).
CD’s letter has not been found; however, CD had obviously made reference to his own work on phyllotaxy, carried out in May and June 1863, in which he sought to account for the series of fractions expressing the angles of divergence between successive leaves on the stems of plants. CD considered that he had ‘signally failed’ in his attempt to explain this phenomenon (see letter to Asa Gray, 26 June [1863]). See also letter to J. D. Hooker, 29 May [1863] and n. 12. The notes from CD’s work on this subject are in DAR 51: 6–32.

Summary

Discusses leaf form and phyllotaxy; clarifies a part of his paper ["On a protomorphic phyllotype", Atlantis (1863)].

Letter details

Letter no.
DCP-LETT-4236
From
George Sigerson
To
Charles Robert Darwin
Sent from
Dublin
Source of text
DAR 177: 162
Physical description
3pp

Please cite as

Darwin Correspondence Project, “Letter no. 4236,” accessed on 11 December 2018, http://www.darwinproject.ac.uk/DCP-LETT-4236

Also published in The Correspondence of Charles Darwin, vol. 11

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