To J. D. Hooker 31 March 
Down Bromley Kent
My dear Hooker
I have been a shameful time in returning your documents,1 but I have been very busy scientifically & unscientifically in planting.— I have been exceedingly interested in the details about the Galapagos Islds —I need not say that I collected blindly & did not attempt to make complete series, but just took every thing in flower blindly.— The Flora of the summits & bases of the islands appear wholly different; it may aid you in observing, whether the different islds have representative species filling the same places in the œconomy of nature, to know, that I collected plants from the lower & dry region in all the islds ie in Chatham, Charles, James & Albemarle (the least on the latter); & that I was able to ascend into the high & damp region only in James & Charles islands; & in the former I think I got every plant then in flower.— Please bear this in mind in comparing the representative species.—2 (You know that Henslow has described a new Opuntia from the Galapagos).—3
Your observations on the distribution of large mundane genera, have interested me much; but that was not the precise point, which I was curious to ascertain;—it has no necessary relation to size of genus (though perhaps your statements will show that it has)—it was merely this; suppose a genus with ten or more species, inhabiting the ten main botanical regions, should you expect that all or most of these ten species would have wide ranges (ie were found in most parts of) in their respective countries. To give an example the genus Felis is found in every country except Australia, & the individual species generally range over thousands of miles in their respective countries: on the other hand no genus of monkey ranges over so large a part of the world & the individual species in their respective countries seldom range over wide spaces. I suspect, (but am not sure) that in the genus mus (the most mundane genus of all mammifers) the individual species have not wide ranges, which is opposed to my query.—4
I fancy from a paper by Don,5 that some genera of grasses, (ie Juncus or Junceæ) are widely diffused over world, & certainly many of their species have very wide ranges— in short it seems, that my question is whether there is any relation between the ranges of genera & of individual species, without any relation to the size of the genera.— It is evident a genus might be widely diffused in two ways. 1st by many different species, each with restricted ranges, & 2d by many or few species with wide ranges.— Any light, which you cd throw on this I shd be very much obliged for. Thank you most kindly, also, for your offer in a former letter to consider any other points; & at some future day I shall be most grateful for a little assistance, but I will not be unmerciful.—
Swainson has remarked (& Westwood contradicted) that typical genera have wide ranges:6 Waterhouse, (without knowing these previous remarkers) made to me this same observation:7 I feel a laudable doubt & disinclination to believe any statement of Swainson’s, but now Waterhouse remarks it, I am curious on the point. There is, however, so much vague in the meaning of “typical forms” & no little ambiguity in the mere assertion of “wide ranges”, (for zoologist seldom go into strict & disagreeable arithmetic, like you Botanists so wisely do)8 that I feel very doubtful, though some considerations tempt me to believe in this remark.—9 Here again if you can throw any light, I shall be much obliged.— After your kind remarks, I will not apologise for boring you with my vague queries & remarks.—
Hamilton in his last Anniver. Geograph. Address refers to Leibmann’s researches of the Alpine Flora of Mexico;10 I mention this for the bare chance of your not having heard of him or his works, whatever they may be.—
I saw Smith & Elder the other day; & he told me he much regretted he could not make an agreement with you; but if you shd alter your plans, he shd be most happy and honoured by any fresh agreement with you—
Believe me | Very truly yours | C. Darwin
Thanks for JDH’s interesting details about the Galapagos.
Clarification of CD’s query about the relationship between the range of a genus and the ranges of its constituent species.
Please cite as
Darwin Correspondence Project, “Letter no. 744,” accessed on 26 April 2017, http://www.darwinproject.ac.uk/DCP-LETT-744