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Darwin Correspondence Project

From Daniel Oliver   12 March 1864

Royal Gardens Kew

12 March/64

My dear Sir,

With regard to your query as to the tendril of Passiflora being ‘a modified flower with its peduncle’,1—I see no objection which would apply to so terming it further than would apply—for example—to terming a stamen a modified petal. And yet perhaps there is even a greater objection. For tho’ a stamen may be called a modified petal,—a petal may with almost equal justice be called a modified stamen.

They are both modifications of a leaf—neither a foliage—nor a flower leaf, but of the ideal leaf which is the key to the homology of all foliar organs whether we call them leaves—simply, or sepals or petals or stamens or carpels or mere scales.2

A flower is an axial whether axillary or terminal in position does not matter.3 organ in as much as it is always borne upon an axis but it is by special modification of foliar organs that its character as a flower is determined;— therefore it may be more correctly spoken of as a foliar organ—or collection of foliar organs.4

Since the tendril does not exhibit any foliar appendages,—since foliar organs do not give it it’s character as a tendril—I think it (the tendril) may be more correctly spoken of as a modified branch or axis than a modified flower. I refer to the tendril of the Passion-flower, which your son’s interesting drawings5 seem to me to shew must be an axial—& at the same-time an axillary—organ.

The vine tendril is axial but not axillary. 6

In a month or so if you take the trouble to look at a branch of Lime tree7 in flower you will find that the leaves bearing the flowering peduncles bear also in their axils a minute second bud—which is a nesting bud, to be developed in the following year. In Passiflora it wd. seem that the 2nd bud is a flower-bud.

As to the distinction between a ‘peduncle’ & midrib of a leaf, or between a branch & a petiole.—8 From the constant contrast in which axial & foliar organs stand nearly all through flowering plants one cannot but think that there is morphologically an ‘essential distinction’ between them, though sometimes this distinction shades off & is lost. Between however a peduncle & a branch there is no essential distinction. They are both axial.9

It is true that leaves do sometimes produce buds, but this does not affect the general question at all, I think. In the same way single cells—or rather globules of cell-contents in lower plants—escaping from vegetative cells serve as buds, settle down & grow (zoospores of algae).

The Tecoma I shall bear in mind.10

Ever my dear Sir | Very sincerely yours | Danl. Oliver

CD annotations

On cover: ‘On Passiflora’; ‘Tendrils & Cucurbitaceæ’; ‘Oliverpencil


Oliver’s reference to ‘the ideal leaf’ and his responses to CD’s queries on the origin of tendrils suggest the possibility that he had been influenced by Naturphilosophie. Although Oliver often provided CD with references to works from the continent (see, for example, Correspondence vol. 11, letter from Daniel Oliver, 27 November 1863 and nn. 6–8), it is uncertain whether he had been influenced by German botanists who paid tribute to Johann Wolfgang von Goethe’s Die metamorphose der Pflanzen [The metamorphosis of plants] (Goethe 1790). See Junker 1989 and Jardine et al. eds. 1996, pp. 236–8. See also n. 9, below.
Oliver wrote the words ‘whether … matter.’ at the bottom of the page and keyed them to this place in the text.
An axial structure or ‘stem-structure’ is a structure formed on the same axis as the stem (see memorandum from Daniel Oliver, [28 January – 8 February 1864]). In his Lessons in elementary botany (Oliver 1864b), p. 67, Oliver wrote: ‘Buds borne in the axils of leaves are axillary; those which terminate a stem or branch, and which, after a winter’s rest in our climate, renew the shoot, are terminal.’ See also letter to Daniel Oliver, 11 March [1864] and n. 7.
See William Erasmus Darwin’s drawings in the enclosure to the letter to Daniel Oliver, 11 March [1864].
See letter to Daniel Oliver, 11 March [1864] and nn. 8 and 9, and n. 4, above.
Lime trees are also known as linden trees (Tilia).
See letter to Daniel Oliver, 11 March [1864] and n. 10; see also n. 9, below.
In ‘Climbing plants’, CD concluded that although all tendrils performed identical functions, they consisted of modified leaves, or modified flower-peduncles, or possibly modified branches and stipules (‘Climbing plants’, pp. 110–11); he also commented: ‘we can hardly avoid asking, whether the difference between foliar and axial organs can be of so fundamental a nature as is generally supposed to be the case’ (ibid., pp. 113–14). A note (ibid., p. 114), referred the reader to Herbert Spencer’s argument (Spencer 1864–7, 2: 37–43) that there was no fundamental distinction between foliar and axial organs; Spencer implied (p. 43), however, that the ‘current morphological creed’ favoured this distinction, which resulted from Goethe’s imposition of ideal forms upon nature. See also n. 2, above.


‘Climbing plants’: On the movements and habits of climbing plants. By Charles Darwin. [Read 2 February 1865.] Journal of the Linnean Society (Botany) 9 (1867): 1–118.

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

Goethe, Johann Wolfgang von. 1790. Versuch die Metamorphose der Pflanzen zu erklären. Gotha: Carl Wilhelm Ettinger.

Junker, Thomas. 1989. Darwinismus und Botanik. Rezeption, Kritik und theoretische Alternativen im Deutschland des 19. Jahrhunderts. Stuttgart: Deutscher Apotheker Verlag.

Spencer, Herbert. 1864–7. The principles of biology. 2 vols. London: Williams & Norgate.


Discusses homologies of plant organs.

The passion-flower tendril should be considered a modified branch rather than a modified flower. Considers the distinction between the peduncle and the leaf midrib.

Letter details

Letter no.
Daniel Oliver
Charles Robert Darwin
Sent from
Source of text
DAR 157.2: 103
Physical description
5pp †

Please cite as

Darwin Correspondence Project, “Letter no. 4425,” accessed on 25 January 2022,

Also published in The Correspondence of Charles Darwin, vol. 12