From J. D. Hooker   31 July 1866

Kew

July 31/66

Dear Darwin

Is there an evidence that the South of England & of Ireland, were not submerged during the Glacial Epoch, when the W. & N. of England were Islands in a glacial sea? And supposing they were above water, could the present Atlantic & N.W. of France Floras we now find there, have been there during the Glacial Epoch?— yet this is what Forbes demands, p 346. At p 347 he sees this objection & wriggles out of his difficulty by putting the date of the Channell “towards the close of the Glacial Epoch”1

What does Austin make the date of the Channell—ante or post glacial?2

Origin Ed III. top of p. 344, how can the breaking of an isthmus give rise to an irruption of new inhabitants?3

I think you are wrong in Origin in implying that the true character of Insular Flora is altogether (or almost) due to herbaceous forms of nearest continent becoming arboreous: though the latter is a strong element too. N. Zealand is a heavy case to the contrary.4 Is DeCandolle right in saying Trees have restricted ranges?5 it is quite the contrary with Pines, Oaks, Beeches, Birches

Thanks for yours just received, which I should like to discuss with you—6 I had before your main arguments, quite clear, but you now send me some important developements.

You must not suppose me to be a champion of Continental Connection, because I am not agreeable to transoceanic migration.7 I have no fixed opinion on the subject—& am much in the state regarding this point, that the Vestiges left me in regarding species.8 What we want is, not new facts, but new ideas analogous to yours of Natural selection in its application to origin— Either hypothesis appears to me well to cover the facts of oceanic Floras, but there are grave objections to both, Botanical to your’s, Geological to Forbes.9

I intend to discuss the point with as little prejudice as I can at Cambridge10—in fact to d—d both hypotheses, or if you like to d—n Ed. Forbes & double d—n yours! for I suppose that is how you will take my fair play. I own that it is most disgusting to have no side, & I cannot tell you how it dispirits me with the whole thing. I shall make up for it by blessing Nat. selection & Variation—& they shall be blest—as necessary to either hypothesis, & therefore proving them to be twice as right as if it only fitted one!11

By saying mountains south of Pyrenees I spoke foolishly. & should have said of North shore of Mediterranean.12 Boissier gives a capital list—. of Grenadan alpines common to North.—13 I forgot all about S. Spain having mountains— I referred to Appenines, Mts of Sardinia & of Atlas, in which I think no alpine plants occur, I think.

The absence of any alpine or subalpine plant of Spain in Madeira or Canaries puzzles me greatly, as they must have been Islands in your glacial sea (there is a sneer for you) & yet you must expect it from there being no boulders.14

?Have you anywhere stated that you regard the old elements of Madeira flora as remains of Tertiary epoch?15

I quite grant that the oldest forms have best chance of being developed into Trees.

I should like to look for old moraines on Pico. Erica Daboeci, a native of W. Ireland & Asturias, being common in two Islands, & Calluna on 3 are staggering facts.16

With regard to the specific differences between Porto Santo & Madeira, it seems pretty much most marked in shells,17 & they do seem to change very fast under some circumstances. Of course I should include them in the same continent: & should have thought its peculiarities quite as good evidence of the sunk continent theory as of the reverse— Two adjacent lands sink, gradually, till all that remains of one is a barren sunburnt rock, of the other a lofty moist wooded mountain. I should expect the organisms common to both, to be most changed by the struggle in the smaller & drier area.

The Azorean Flora is almost identical with the Madeiran, It has about 30 endemic species & varieties, which with 25 Maccronesian species,18 make 55 sp. out of about 350 difft. from Europe— Though upwards of 500 miles N. of Madeira & with Mts. 7000 ft high, it contains only 3 plants of more boreal character than Madeira, viz. Viola palustris & Calluna vulgaris, both which however reached Grenada, & Littorella lacustris, a more boreal water plant which may have brought to the Lake by Gulls’ feet— Considering how much nearer these Islands are to Newfoundland on one hand & Britain on the other, this absence of more plants of either country seems marvellous.19 It also appears strange to me that Madeira should have contributed 25 of her otherwise endemic forms to such a distance & that they should have kept their characters.

The Islands want better exploring however.

Of course you know that the sea currents all set from the Atlantic Islands to the Mediterranean,—but that is a trifle to a sound migrationist!20

We have not Duvernoya.21

Acropera will be sent tomorrow to be left at Bromley station.22

Ever yr aff | J D Hooker

CD annotations23

1.1 England] underl pencil
1.1 Ireland … Epoch, 1.2] scored pencil; ‘Yes’ added pencil
1.3 could the … Epoch?— 1.4] scored pencil; ‘No’ added pencil; ‘as soon believe that those of France cd not exist on summit of Mt B’ added pencil
2.1 What … glacial?] scored pencil; ‘I forget’ added pencil
3.1 Origin … inhabitants? 3.2] doubled scored pencil
4.4 Is DeCandolle … ranges?] double scored pencil
6.1 You … Connection,] scored pencil; ‘Coral Islets’ added pencil
6.6 but there … to Forbes. 6.7] scored pencil; ‘I shall much like to hear Botanical reasons against occasional migration— Remember [illeg]’ added pencil
6.7 Botanical] underl pencil
7.5 thing.] closing square bracket added after, pencil
9.1 or Canaries] ‘or’ del pencil
10.1 ?Have you … epoch? 10.2] double scored pencil
13.1 it seems … shells, 13.2] scored pencil
14.1 It has … than Madeira, 14.4] scored pencil; ‘No doubt great difficulties’ added pencil
14.7 Considering … other, 14.8] scored blue crayon
16.1 Of course … Mediterranean 16.2] double scored pencil
Top of letter: ‘Book— Acropera’ pencil
1
Hooker refers to Edward Forbes and to Forbes 1846. Forbes argued that the flora of Kent had migrated from north-western France (Forbes 1846, p. 346), and noted that the distinct floras of south-western England and south-eastern Ireland was closely related to that of the Channel Islands and the extreme west of France (ibid., p. 347; see also ibid., p. 338). Although Forbes favoured pre-glacial migrations for these flora, he conceded that their survival might have been endangered later by low temperatures around the glacial sea in the area of the English channel. Forbes went on to suggest their more recent migration, and that the English Channel might be of post-Pliocene origin (ibid., p. 347; see also J. D. Hooker 1866a, p. 50, for Hooker’s summary of Forbes’s hypothesis).
2
According to Robert Alfred Cloyne Godwin-Austen, the English Channel was formed during the Pleistocene period, that is in the post-Pliocene, after the coldest phase of the Glacial Period (Austen 1849, pp. 87–9, 95; see also Imbrie and Imbrie 1979, pp. 90–2).
3
The passage at the top of page 344 in the third edition of Origin was altered by CD in the fifth edition, where he specified that the new inhabitants irrupted ‘into an adjoining sea’ after the breaking of an isthmus (Origin 5th ed., p. 390).
4
The reference is to Origin, p. 392 (see letter to J. D. Hooker, 30 July [1866] and n. 9). In his lecture on insular floras, Hooker alluded to the absence of gum (eucalyptus) trees in New Zealand and their presence in Australia as an example of an island’s tree population being derived independently of the adjacent continent (J. D. Hooker 1866a, p. 75); however, Eucalyptus does not include any herbaceous species (Mabberley 1997).
5
In Origin, p. 392, CD wrote: ‘trees, as Alph. De Candolle has shown, generally have, whatever the cause may be, confined ranges’. The reference is to A. de Candolle 1855, 1: 527–32.
7
CD and Hooker had long disagreed about the geographical distribution of species, continental extensions, and occasional transport: see letter to Charles Lyell, 15 February [1866], n. 6.
8
The reference is to Vestiges of the natural history of creation ([Chambers] 1844); for Hooker’s initial reactions to it, see Correspondence vol. 3, letter from J. D. Hooker, 30 December 1844. For an analysis of the arguments concerning the origin of species in [Chambers] 1844, see Secord 2000, pp. 104–8.
9
In his lecture, Hooker cited CD on the persistence during recent geological periods of islands and continents, and of the general form of the sea bed, as a geological argument against continental extension (J. D. Hooker 1866a, p. 51). As botanical evidence against CD’s doctrine of occasional transport as the means by which island floras originated, Hooker referred to a number of rare plants that were unique to some islands. Hooker noted a further botanical objection to CD’s doctrine of occasional transport was that certain plants on Kerguelen’s Land were also to be found in Tierra del Fuego but not in South Africa or New Zealand, both of which are closer to Kerguelen’s Land (J. D. Hooker 1866a, pp. 50–1, 75).
10
Hooker was to deliver his lecture on insular floras (J. D. Hooker 1866a) at Nottingham rather than Cambridge.
11
In his lecture, Hooker evaluated CD’s and Forbes’s hypotheses concerning the derivations of the floras of oceanic islands, and urged that a distinction be made between CD’s doctrines of occasional transport and of variation and natural selection; he concluded in his summary that CD’s hypothesis of migration across the sea was more satisfactory than Forbes’s (J. D. Hooker 1866a, pp. 50–1, 75).
14
The absence of alpine and subalpine plants in Madeira had been discussed in the letter from J. D. Hooker, [24 July 1866], and the letter to J. D. Hooker, 30 July [1866]. Hooker’s reference to the absence of erratic boulders apparently implies his belief that plants could not have arrived on the islands by means of icebergs; in Origin, p. 363, CD had argued on the basis of reported evidence of erratic boulders that some of the flora of the Azores had derived from progenitors that had been transported there by icebergs.
15
In Origin, CD had cited Oswald Heer on the similarity between the flora of Madeira and the tertiary flora of Europe (see letter to J. D. Hooker, 30 July [1866] and n. 10).
16
Hooker refers to the island of Pico in the Azores; moraines would provide evidence of former glacial action (see also n. 14, above). Daboecia azorica (a synonym of D. cantabrica subsp. azorica, St Dabeoc’s heath) is native to the Azorean islands of Foyal and Pico (Underhill 1971, p. 203). In his lecture, Hooker noted the presence of St Dabeoc’s Heath (Daboecia sp.) and Calluna vulgaris in the Azores and their absence from Madeira and the Canaries; Hooker also stated that Daboecia only occurred elsewhere in the west of Ireland, and in the Pyrenean region (J. D. Hooker 1866a, p. 27).
17
Hooker mentioned differences between the floras of Madeira and Porto Santo in his lecture (J. D. Hooker 1866a, p. 7). On the differences between the land shells of Madeira and Porto Santo, see also Origin, pp. 402–3. See letter to J. D. Hooker, 30 July [1866].
18
Macaronesia is a biogeographical region that includes the archipelagos of the Azores, Madeira, the Salvage Islands, the Canary Islands, and the Cape Verde Islands (Sunding 1979).
19
In his lecture, Hooker noted that a similar number of species of American plants were represented in the floras of the Azores, Madeira, and the Canary Islands, despite the relative proximity of the Azores to America. He also noted an unexpected paucity of boreal plants. (J. D. Hooker 1866a, p. 27.) Viola palustris is alpine marsh violet; Calluna vulgaris is heather; Littorella lacustris is a synonym of L. uniflora, shoreweed.
20
In his lecture, Hooker asserted his belief that the plants of the Atlantic islands had originally migrated from the continent of Europe, but also noted that the sea currents favoured transport in the opposite direction (J. D. Hooker 1866a, pp. 50, 75).
21
The genus Duvernoya (family Acanthaceae) is now subsumed within Justicia (Mabberley 1997). However, the reference is probably to the book for which CD had asked Hooker (see letter to J. D. Hooker, 30 July [1866] and n. 16). CD was writing the second volume of Variation, in which there is a reference to Duvernoy 1834 (Variation 2: 137 n. 67).
22
For CD’s earlier interest in Acropera, see Correspondence vols. 9–12. Acropera is a genus of tropical orchids now subsumed within Gongora (Bailey and Bailey 1976).
23
CD’s annotations are notes for his letter to Hooker of 3 and 4 August [1866].

Please cite as “DCP-LETT-5168,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-5168