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Letter 1664

Bunbury, C. J. F. to Darwin, C. R.

10 Apr 1855

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    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.

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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 ft, towards the head waters of the Orange River, he describes the vegetation as very poor, & such as is characteristic of an arid soil & climate. The extreme aridity of all that inland part of South Africa appears to be partly owing to the chains of mountains bordering the coast (especially the Outeniqua or Zitzikamma mountains on the S. coast,) wch catch the vapours brought by the sea-winds, & receive all their moisture. I crossed that southern coast-chain at Cradock's Kloof, & was struck with the comparative luxuriance of the vegetation on the seaward side; but the plants were all of characteristic Cape genera, such as Restio, Pelargonium, Helichrysum, Penæa, Protea, Antholyza. That pass however is of moderate height, probably under 3000 feet. The height of Table Mountain itself (3580 ft) is perhaps hardly sufficient to entitle us to expect any thing like a properly alpine vegetation on its summit. It is a height corresponding to the middle of the forest zone in the Canaries. It is rather remarkable, considering the frequent clouds & abundant moisture on the top of Table Mt, that it should be so entirely bare, not only of trees, but even of moderate-sized shrubs; this is probably owing to the violence of the winds. One characteristic, as well as I remember, of the summit vegetation of Table Mt is the absence of the succulent plants, such as Mesembryanthemums, Crassulaceæ, & succulent Euphorbias, which belong more particularly to dry, parched, sun-burnt situations. The Crassula coccinea is an exception. There are a good number of species, particularly of Orchideæ, peculiar (as far as is hitherto known) to the top of that mountain, but they are all of thoroughly S. African genera. When I am at home, with easier opportunities of reference, I hope I may be able to give you some more information on this point. I do not know of any genera confined to that mountain. Not a few species, again, (& species peculiar to the Cape) are common to the summit of the mountain & to much lower levels. I wish I had noted these & various other points more thoroughly when I was there; indeed I never can investigate any thing connected with the Floras of the Cape or of South America, without deeply regretting that I did not make better use of my opportunities. You may like, however, to have one or two instances of what I last mentioned. Erica coccinea grows on the summit & at the foot of Table Mountain; Erica spumosa, on the summit of the mountain, & on the sandy table-land behind Simons Town, which indeed is a prolongation of the same mountain-mass, but less than 1000 ft above the sea; Protea cynaroides, on the summit, & on the low sandy flats between Table Bay & False Bay; Penæa mucronata, the same; Schizæa pectinata, the same; Todea Africana, from the summit down to the Platte-Klip, where the ravine opens out. These last two are Ferns.

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 ft high; it appeared however so constantly free from clouds, (& this was in the autumn & beginning of winter,) that I should suspect it would be very dry, & consequently unproductive.

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.

    Footnotes Add

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    f1 1664.f1
    Bunbury 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.
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    f2 1664.f2
    Karl Ludwig Philipp Zeyher. See Zeyher 1846 and Zeyher and Burke 1845–6.
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    f3 1664.f3
    A genus in which it was considered very difficult to separate species from varieties.
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    f4 1664.f4
    CD 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.
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    f5 1664.f5
    Cited in Natural selection, p. 552, n. 3.
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    f6 1664.f6
    Cited in Natural selection, p. 566. See also n. 7, below.
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    f7 1664.f7
    A 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.
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