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Darwin Correspondence Project

To J. D. Hooker   1 December [1856]1

Down Bromley Kent

Decr 1st

My dear Hooker

I am become a good deal interested in crossing speculations, though I can come to no certain conclusion.— With respect to Trees, which from number of flowers on same individual offer, considerable difficulty to the probability of crossing, I want to know whether the following would cost you much trouble, & whether you feel the least interest on the point.2 I have had copied in good hand a list in order, divided into Families, of the 700–800 New Zealand plants.3 Now I have no idea how far you have in your mind the memory of the N.Z plants: if distinctly it would not take you half an hour to go over the list (as many Families might be skipped) & mark with pencil cross the Trees & double Pencil cross those which were also mono- or diœcious or polygamous.4 I tried to do it, but broke down in not being able to decide between bushes & trees, & this must be arbitary.— I have done the few Trees of England, taking Loudon as rule what to call trees & what bushes, & you will see result.5 If N. Zealand with so different a Flora gave at all same result, it would appear probable that there was some connection between trees & the separation of sexes (which wd. favour crossing).—6 Loudon calls the Viburnum, Box, Arbutus & Juniper Bushes.—

I think in your N. Zealand Flora you have given the number of plants of all kinds with separated sexes, which would have to be considered in the result.—

Now it will wholly depend on the state of your memory whether this would be worth doing, as it would by no means be worth your having to consult your own Flora.— What say you? Shall I send the M.S. list? Can you tell me genus of enclosed seed, which was in Birds Dung & has since germinated.—7

Ever yours | C. Darwin


Dated by the reference to the crossing of trees, also discussed in the letters to George Bentham, 26 November [1856] and 30 November [1856].
See letters to George Bentham, 26 November [1856] and 30 November [1856]. CD addressed the question of the crossing of trees in Natural selection, pp. 61–2.
CD’s list, in the hand of an amanuensis, is now located in the back of CD’s copy of the introductory essay of J. D. Hooker 1853–5, in the Darwin Library–CUL.
CD’s results are given in Natural selection, pp. 61–2. He refers to Loudon 1842.
CD’s point was that a hermaphrodite tree would have so many flowers that any crossing that took place would be with a flower from the same tree. If the flowers were all of one sex on a tree, crossing could only take place between flowers of different trees (see Natural selection, p. 61).
Hooker apparently lost the seed (see letter to J. D. Hooker, 24 December [1856]). Hooker had previously identified other seeds from birds’ dung for CD (see letter from J. D. Hooker, 22 November 1856).


Hooker, Joseph Dalton. 1853–5. Flora Novæ-Zelandiæ. 2 vols. Pt 2 of The botany of the Antarctic voyage of HM discovery ships Erebus and Terror, in the years 1839–1843, under the command of Captain Sir James Clark Ross. London: Lovell Reeve.

Loudon, John Claudius. 1842. An encyclopaedia of trees and shrubs; being the arboretum et fruticetum Britannicum abridged. London.

Natural selection: Charles Darwin’s Natural selection: being the second part of his big species book written from 1856 to 1858. Edited by R. C. Stauffer. Cambridge: Cambridge University Press. 1975.


Questions JDH on separation of sexes in trees in New Zealand flora.

Letter details

Letter no.
Charles Robert Darwin
Joseph Dalton Hooker
Sent from
Source of text
DAR 114: 185
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 2008,” accessed on 8 May 2021,

Also published in The Correspondence of Charles Darwin, vol. 6