Suggests affinities of the U. S. flora that he considers would be worth investigating. Wants to know the ranges of species in large and small genera.
Questions AG on naturalised plants; whether any are social in U. S. which are not so elsewhere and how variable they are compared with indigenous species. Would like to know of any differences in the variability of species at different points of their ranges and also the physical states of plants at the extremes of their ranges.
Down Bromley Kent
My dear Dr
I have received your very kind note of Ap.
I should like to see the genera of the U. States, say 500 (excluding Arctic
& Alpine) divided into 3 classes, with the proportions given, thus,
There is an interesting discussion in Decandolle (about p. 503 to 514) on the relation of the size of Families to the average range of the individual species; I cannot but think from some facts which I collected long before De Candolle appeared, that he is on wrong scent in having taken Families (owing to their including too great a diversity in the constitution of the species), but that if he had taken Genera, he would have found that the individual species in large genera range over a greater area than do the species in small genera: I think if you have materials that this would be well worth working out; for it is a very singular relation.—
With respect to naturalised plants; are any social with you, which are not so
in their parent country? I am surprised that the importance
of this, has not more struck Decandolle. Of these naturalised plants are any or many
more variable in your opinion, than the average of your U.S. plants: I am aware
how very vague this must be: but De Candolle has stated that the naturalised plants do
not present varieties; but being very variable &
presenting distinct varieties seems to me rather a different case: if you would kindly
take the trouble to answer this question, I
With respect to such plants, which have their southern limits within your area, are the individuals ever or often stunted in their growth or unhealthy: I have in vain endeavoured to find any Botanist who has observed this point; but I have seen some remarks by Barton on the trees in U.S. Trees seem in this respect to behave rather differently from other plants.—
It would be a very curious point, but I fear you would think it out of your Essay, to compare the list of European plants in Tierra del Fuego (in Hooker) with those in N. America; for without multiple creation, I think we must admit that all now in T. del Fuego, must have travelled through N. America, & so far they do concern you.—
The discussion on Social plants (vague as the term & facts are) in De candolle
strikes me as the best, which I have ever seen: two points
strike me as eminently remarkable in them; that they should ever be social close to
their extreme limits; & secondly that species having an extremely
confined range, yet shd
There is one other point, on which I individually
I suppose your Flora is too great; but a simple list in close columns in
small type of all the species, genera, &
I am sure I have given you a larger dose of questions than you bargained for, & I have kept my word & treated you just as I do Hooker. Nevertheless if anything occurs to me during the next two months, I will write freely, believing that you will forgive me & not think me very presumptuous.
My dear Dr
I have reread this letter & it really is not worth sending, except for my own sake.: I see I forgot in beginning to state that it appeared to me that the 6 heads of your Essay included almost every point which could be desired, & therefore that I had little to say.—
How well De Candolle shows the necessity of comparing nearly equal areas for proportion of Families!
(Excuse this poor paper I am run short)
- f1 1863.f1Dated by the suggestions CD makes in this letter, which were incorporated into A. Gray 1856–7 (see n. 3, below).
- f2 1863.f2Gray's letter has not been found. CD's previous letter to Gray had been written in August 1855 (see Correspondence vol. 5, letter to Asa Gray, 24 August ).
- f3 1863.f3Gray was preparing the first part of his paper ‘Statistics of the flora of the northern United States’ (A. Gray 1856–7). In the published version, Gray acknowledged, without mentioning his name, CD's contribution to the work: ‘While engaged in the preparation of a second edition of the Manual of the Botany of the Northern United States, I was requested by an esteemed correspondent, upon whose judgment I place great reliance, to exhibit, in a compendious and convenient form, the elements of flora I was occupied with.’ (A. Gray 1856–7, p. 204).
- f4 1863.f4Gray generally followed this recommendation and devoted a separate section to a discussion of the alpine and sub-alpine flora of the United States (A. Gray 1856–7, pp. 62–76).
- f5 1863.f5A. de Candolle 1855, 2: 642–5, 703–4. Gray agreed with this point, stating that the admission of introduced species into the comparison ‘seriously vitiates our conclusions’ (A. Gray 1856–7, p. 212).
- f6 1863.f6This information is tabulated in A. Gray 1856–7, pp. 215, 217–24, and 226–9.
- f7 1863.f7Gray attempted a ‘Comparison of the flora of the northern United States with that of Europe in respect to the similar or related species’, in spite of the difficulties such an enterprise entailed ‘owing to the impossibility of estimating the degrees of resemblance among species, or at least of expressing them in any precise or definite way, or bringing shades of difference to any common standard.’ (A. Gray 1856–7, p. 78).
- f8 1863.f8Gray stated that he found this comparison problematic. He therefore settled on taking species rather than genera for his comparison and did not attempt ‘anything beyond an enumeration’ of species in the three classes (A. Gray 1856–7, pp. 80–3).
- f9 1863.f9A. de Candolle 1855.
- f10 1863.f10Bound in CD's copy of A. de Candolle 1855, 1: pp. 528–9, is a note, dated 1 May 1856, made by CD when studying Alphonse de Candolle's discussion of the ‘area of species according to families’ (A. de Candolle 1855, 1: 501–32). After working through his own calculations made on data for the Cape flora of South Africa, CD concluded by stating: ‘So that nothing can be inferred safely from these results. Families [’Genera‘ del] being too large.—’ See J. Browne 1980.
- f11 1863.f11Gray followed this suggestion explicitly. After mentioning that Candolle's calculations were founded upon families, he stated: ‘To be of any value, at least upon our limited scale, the comparison should be made with genera, as Mr. Darwin suggests; and from some investigations of his own, this sagacious naturalist inclines to think that species in large genera range over a wider area than the species of small genera do.’ (A. Gray 1856–7, p. 77). For the most part, Gray's calculations tended to confirm CD's generalisation, particularly when the woody plants were examined, although Gray noted that the converse of the proposition ‘does not tell in the same way’ (A. Gray 1856–7, p. 381).
- f12 1863.f12Gray addressed this question only indirectly. As he stated, ‘properly to discuss this and kindred topics would require a great amount of detailed investigation, and would expand these articles into a treatise.’ (A. Gray 1856–7, p. 389). CD had explained his interest in this point in his letter to J. D. Hooker, 14 November  (Correspondence vol. 5).
- f13 1863.f13A. de Candolle 1855, 2: 607–8. The passage is marked in CD's copy in the Darwin Library–CUL.
- f14 1863.f14Probably Barton 1809.
- f15 1863.f15European plants in Tierra del Fuego are not separately listed in Flora Antarctica (Hooker 1844–7), but presumably CD hoped Gray would extract them from the Fuegian flora details.
- f16 1863.f16A. de Candolle 1855, 1: 457–73.
- f17 1863.f17Wahlenberg 1824–6 on which CD commented in his reading notebook: ‘most curious passage about species not varying in North.’ (Correspondence vol. 4, Appendix IV, *128: 169).
- f18 1863.f18A. de Candolle 1855, 2: 1154.