Responds to CD's questions about mountain vegetation of the Cape of Good Hope. The distribution of some plants provides problems for both migration and special creation hypotheses.
17 Queens Road West
April 10, 1855
My dear Darwin,
I was much delighted by your letter of questions, & I hope you will never flinch from asking me as many as you like;—whether I shall always be able to answer them, is another matter, but at least I can try.
First, as to the mountain vegetation of the
Cape. This is a subject on which I wish that I possessed
more information. All I have been able to find, is an observation (in Hooker's
London Journal of Botany, vol. 5) by Zeyher, an
accurate botanist, & one who has resided long in that country. He says that the
mountains in the interior of the Cape colony,—the Sneeuwberg, Roggeveld,
& Nieuwveld mountains,—have, even in their higher regions, an
excessively dry atmosphere, & consequently their vegetation has a
Karroo-like character, quite similar to that of the barren & desert
regions several thousand feet below. What is called a Karroo vegetation consists of
succulent plants (Mesembryanthemums &c) & hard stunted shrubs, but no
grass or Heaths. The actual summits of the mountains, Zeyher says, are covered with
Grasses. At the height of 5000 f
The Amatola, & other mountains of Caffraria, remain
to be examined. I am very sorry that when I was on the frontier I did not visit the
Winterberg, which is supposed to be 8000 f
Secondly, as to Rubus. This is a genus very widely spread, & there are several tropical species. One, very like our common Brambles in general appearance, grows at Rio de Janeiro, at a very moderate elevation, among Melastomaceæ & other thoroughly tropical forms. There are others in the interior of Brasil, & Humboldt, I think, mentions Rubi in the valley of Caraccas. There are however, doubtless, genera which occur at the Cape & likewise in the northern temperate zone, but not in the intermediate tropical regions. Erica is a very striking instance; Gladiolus is another (at least I do not know of any tropical Gladioli); & I have no doubt there are others, but I do not at this moment recall them to mind. Protea, a most characteristic Cape genus, has one solitary species in the northern hemisphere, namely in the highlands of Abyssinia. By the way, I recollect several instances of the converse case to that of Erica, that is, genera which have their head quarters in the northern temperate zone, but are represented at the Cape by one or a few distinct species; such are Dianthus, Silene, Statice, Frankenia.— The most puzzling fact in botanical geography that I know of, is one mentioned by Hooker; that Myrsine Africana is found at the Cape, in Abyssinia, & in the Azores, & nowhere else. This appears to me equally inexplicable on either hypothesis, of migration or of separate creation; for one can see no analogy of climate or local circumstances between the Cape & the Azores.
- f1 1664.f1Bunbury had collected plants at the Cape of Good Hope in 1838 and 1839, as described in C. J. F. Bunbury 1848. CD had previously discussed the mountain flora of the Cape with him (see letter to C. J. F. Bunbury, [20 March 1855], n. 2). CD was anxious to know whether the plants belonged to genera usually found in the northern hemisphere or whether they were alpine forms of the African lowland flora. He was investigating the possibility that many of the mountainous parts of the southern hemisphere had been colonised by northern plants during a worldwide cold period. The Cape of Good Hope appeared to be the only exception to CD's theory. See Natural selection, pp. 551–2, and Browne 1983, pp. 123–31.
- f2 1664.f2Karl Ludwig Philipp Zeyher. See Zeyher 1846 and Zeyher and Burke 1845–6.
- f3 1664.f3A genus in which it was considered very difficult to separate species from varieties.
- f4 1664.f4CD was also attempting to gauge whether there had been any migration of southern plants towards the equator during the cold period. See Natural selection, p. 559, in which he cited information taken from C. J. F. Bunbury 1848, p. 218.
- f5 1664.f5Cited in Natural selection, p. 552, n. 3.
- f6 1664.f6Cited in Natural selection, p. 566. See also n. 7, below.
- f7 1664.f7A reference to the discussion of the flora of Fuegia in J. D. Hooker 1844–7, 1: 210. CD's copy of this work (Darwin Library – CUL) is annotated.