# From J. D. Hooker   [15 November 1854]1

Kew

Wednesday

Dear Darwin

On the back of this you have a list of 80 very anomalous genera selected by Bentham—2 I appended 1) the number of species enumerated in Steudel Nomenclator 3 the only catalogue of plants & not a bad one for such purposes & 2) the number of species according to Benthams & my knowledge of the genera, which increases some, diminishes others, & also diminishes the total of species. I append Steudels ratio of species to genera of all plants.— I should suppose however that it would stand considerable reduction & that 1:8 would possibly be a fair estimate or even 1:6.—4

I am working up my Tasmanian Flora5 now, & at the same time making a running catalogue of the Australian plants. There is probably as great specific difference between East & West Australia, as between New Zealand & Australia, this is quite a guess, but right or wrong offers food for speculation. Suppose the sea to cut Australia longitudinally—& to leave species as they are, it would probably leave the northern ends of the two resultant Islands more Botanically alike than the Southern.— But allow the consequent equable climate upon both Islands produced by the intervening ocean to have its effect; & it would theoretically destroy more of the plants peculiar to the Southern (drier) than the Northern (wetter) halves of each, & thus approximate the Botanical features of the Southern parts of each proportionately more than the Northern. also we may assume that all after imports would succeed better in the two humid Islands than upon the one dry one & that the sea being as good as a transporter as the desert the tendency to uniformity would increase— “Under this view disruption produces similarity of Botanical features” & except you call in new creations I do not see how you are to produce any considerable amount of specific difference in two contiguous spots with the same climate consistently with Geological change having any effect at all. The prominent effect of geological change is change of climate & that as it appears to me tends to destroy species & especially peculiar genera—6 Granting even that the existing species are altered preexistent forms, it appears to me that the tendency is to obliteration of forms, for the number of species that will change under change of climate is indefinitely small compared to what will be killed by the same change of climate: the number of species was once infinitely greater than now, or we have new creations

Ever yrs | J D Hooker. diag Steudel Self

1 Ceratophyllum — 8 — 2

2 Cannabis — 1 — 1

3 Oldfieldia — 1 — 1

4 Gyrostemon — 3 — 3

5 Callitriche — 16 — 4

6 Batis — 1 — 1

7 Nepenthes — 7 — 10

8 Sabia — 4 — 7

9 Lacistema — 5 — 8 10 Moringa — 4 — 2 11 Fouquiera — 1 — 2 12 Trigonia — 8 — 8 13 Krameria — 9 — 9 14 Reaumuria — 2 — 2 15 Tetradiclis — 1 — 1 16 Canella — 2 — 1 17 Cneorum — 2 — 1 18 Suriana — 1 — 1 19 Hernandia — 4 — 2 20 Cassytha — 10 — 15 21 Schæffera — 5 — 3 22 Goupia — 2 — 1 23 Balanites — 1 — 1 24 Diapensia — 2 — 1 25 Stilbe — 6 — 6 26 Desfontainia — 1 — 1 27 Retzia — 3 — 1 28 Cyananthus — 3 — 5 29 Codon — 1 — 1 30 Ægiceras — 4 — 2 31 Salvadora — 5 — 1 32 Brunonia — 2 — 2 33 Phryma — 1 — 1 34 Bravaisia — 1 — 1 35 Columellia — 3 — 3 36 Xanthium — 8 — 4 37 Gyrocarpus — 4 — 2 38 Anisophylleia — 2 — 2 39 Gunnera — 8 — 10 40 Diclidanthera — 2 — 2 ————————

1161 1132 Ratio of species to genera in Steudel $\frac{6722}{78005}$ ramme

## CD annotations

1.3 not a bad one] underl pencil
2.1 I am] after‘[’ added brown crayon
2.15 not see how you are to produce 2.16] underl brown crayon
scored brown crayon; ‘{squlreverse question mark]}’ added brown crayon
On list: ‘1’, ‘2’, ‘191 (?)’, ‘2 ?’, ‘1’, ‘1 (?)’, ‘1’, ‘1 (?)’, ‘2.’, ‘1’ added pencil in left margin of first ten lines, with heading ‘No. of genera in Order in Lindley’ pencil, circled pencil

## Footnotes

Dated by a note in CD’s hand headed ‘Nov. 20/54.’ which refers to Hooker’s remarks on the flora of Australia (DAR 205.2: 109). The Wednesday before this date was 15 November. CD made further comments about this letter in a note dated ‘Nov. 30/54/.’ (see n. 4, below).
George Bentham. The list as given by Hooker at the end of the letter contains only 40 items. Hooker may have also enclosed a further list of aberrant genera (DAR 114.4: 222a) compiled at CD’s request (see letter from J. D. Hooker, [3 November 1854], n. 7).
Steudel 1840–1. CD’s copy, lightly annotated, is in the Darwin Library–CUL.
CD pinned the following note (DAR 205.9 (Letters)) to Hooker’s letter: Nov. 30/54/. Bentham remarked to me in regard to his list of aberrant genera, that in fact it was scarcely possible to tell genus from Family, a latter from a higher group. (This shown by 3, 5, 4, 7 having been taken by Quinarians) & I think He said that Bignonia was first a genus, & then when many species were found, it was [‘fo’ del] converted into a Family, with several genera.— Now this causes the greatest, scarcely superable difficulty in ascertaining whether the number of species, be small; for if what wd be an aberrant genus, as long as there were few species, was raised into Family, of course aberrant genera must necessarily have few *species. Will [altered from ‘species: now will’] it not [interl] do to take an [‘n’ added] aberrant [interl] groups, & say whether you call them *genera, or families [above del ‘small or great’] or alliance, yet they [‘are aberrant’ del] include less species even than genera, & a fortiori less than Families do on average.— But then if this be done, it may be said that they are aberrant merely because they have few species: that this alone makes them aberrant.— Nevertheless I still think & so does Bentham, that there is something in it.— See letter to J. D. Hooker, 4 December [1854], for CD’s rephrasing of these comments. In the interval between receiving this letter and letter to J. D. Hooker, 4 December [1854], CD also made the following note (DAR 205.9 (Letters)): Taking Steudel as Standard, there are to each [‘species’ del] genus 672278005=11.6 (Hooker says too much). Whereas Benthams anomalous [interl] genera 40)161 (4.02— *(calculated by Steudel) [added pencil] This is very striking; but then Bentham said something to me about excluding genera with many species.— *see Hookers note with X [added pencil; ‘X’ in brown crayon] [‘I’ del] May it not be said that any anomalous genus with many species wd. be a Family. *For as Bentham remarked there are Families which run each other, so that if you increased number of species in an anomalous genus, this wd. make a Family.— Yet this can be hardly true, for Bentham admitted that in these running together Families, the type of each was very distinct, but yet the type of these anomalous genera, I infer, wd. not be so different *as the types of Different Family [interl in pencil].— Solaneæ & Scrophulariæ case of blending Families.—[pencil]
J. D. Hooker 1855–60.
Hooker refers to CD’s view expressed in his essay of 1844 which Hooker read in 1847 (see Correspondence vol. 4, letter to J. D. Hooker, 8 [February 1847]; letter from J. D. Hooker, [c. 4 March 1847]; letters to J. D. Hooker, [14 March 1847], 7 April [1847], [2 June 1847], and [4 August 1847]). In his essay, CD maintained that geological and topographical changes were an important feature in ‘unsettling’ the reproductive mechanisms of organisms, thereby giving rise to variant offspring (Foundations, pp. 108, 186). Hooker expresses the view that geological changes would, on the contrary, obliterate organisms that were either peculiar to the particular country concerned or specialised in any way.

## Summary

George Bentham’s list of aberrant plant genera. JDH appended the number of species in each genus according to E. G. Steudel’s catalogue [Nomenclator botanicus (1840–1)] and according to JDH and Bentham.

JDH speculates on effect of splitting Australia longitudinally on distribution; it becomes an argument for new creations.

## Letter details

Letter no.
DCP-LETT-1607
From
Joseph Dalton Hooker
To
Charles Robert Darwin
Sent from
Kew
Source of text
DAR 205.9: 386
Physical description
2pp inc ? †, CD note