From Daniel Oliver 12 March 1864
Royal Gardens Kew
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
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.
Please cite as
Darwin Correspondence Project, “Letter no. 4425,” accessed on 6 May 2016, http://www.darwinproject.ac.uk/DCP-LETT-4425