From J. D. Hooker [c. 3 September 1844]1
had all the work with them myself & think he ought to have given them up with the other colls’.— Have you seen Gray’s 1st. number of Mammalia or Richardson’s on fish?:2 the latter is admirable as far as I can judge.
I have a sort of notion that the more varied the temperature is on a given surface the more species it produces—“ceteris paribus”. The campos of central Brazil are, I believe, vastly richer in species than the woods, & every few miles adds new plants. The plains of the Andes are immensely rich in species of plants under the line, much more so than the sea coast.. A mountain immediately gives new vegetable forms, perhaps not so much because its temperature is lower but because its vicissitudes are more remarkable. I argue very much from the absence of new forms in proceeding from Chonos’ Archip. down to Cape Horn. The temp. of the latter is certainly the coldest but it is quite as, if not more equable (I suppose). say that 12 degrees of Lat intervenes,—but go from Devonshire to John O’Groats & what a totally new vegetation is met with, not only have the old forms disappeared, but they are replaced by very numerous new ones. I do not suppose that any trees in the N. Temperate zone have the range in Latitude at the level of the sea that the Beech or Winters Bark have in S. America or the Dimon pine (Dacrydium cupressinum) in New Zealand.
This is a young subject to me, have you thought of it at all?. I shall be most happy to work out any suggestions on the subject.
I am trying very hard to get a month ahead with my book that I may go to Norfolk when my Mother returns.
With kind regards to Mrs Darwin Believe me | Ever yours most truly | Jos D Hooker.
Suggests there is a direct relation between temperature and abundance of plant species.
Please cite as
Darwin Correspondence Project, “Letter no. 774,” accessed on 19 January 2017, http://www.darwinproject.ac.uk/DCP-LETT-774