From J. D. Hooker [4–9 September 1845]1
–translation, though it is rather cool of me to ground my censure upon my own inability to understand parts of it.2
I am exceedingly glad that l’Espece has interested you,3 & will try & get you a copy from Montagne,4 through whom my father received this. I am not inclined to take much for granted from any one treats the subject in his way & who does not know what it is to be a specific Naturalist himself. Those who have had most species pass under their hands as Bentham, Brown, Linnæus, Decaisne & Miquel, all I believe argue for the validity of species in nature: they all direct attention to the cases where salient characters are unimportant, though taken advantage of by the narrow-minded studiers of overwrought local floras, & these facts, thus noticed as cautions to others, are taken up by such men as Gerard, who have no idea what thousands of good species their are in the world. Nature may have both made & muddled species, we never shall know what are species in some genera & what not. Generally cultivation will prove the validity of a species, Gerard says that, “varieties of apples &c are more distinct than many species”, but how soon all revert to crabs: again, the wheat is always adduced as a permanent variety of some unknown plant which ought on that account to rank as a species, but I do not think so, because it will never run wild: it is to me very marvellous that the wheat seed is destroyed by being left in the ground of our country & that we see so little next year on a field that has supported millions of ears, during the present.
Gerard evidently is no Botanist, he talks of having found both Prunus spinosa & Rubus fructicosus without spines: now spines are only abortive branches, & their absence or presence is never, of itself, a Botanical character; as a spine is not an organ per se; & again, no Rubus ever had or ever will have spines: the prickles of Rubus are mere appendages of the cuticle & have no organic connection (like spines) with the pith & wood of the plant: species vary in pricklyness just as they do in hairiness, according to the amount of spines or hairs produced; but they vary in spinyness according to the number of branches that are checked in growth which is much affected by want of moisture.
You are right then to Query that bit about plants developing spines in bad soil; for they only lose the power of nourishing the new leaf buds sufficiently & do not develope a new organ (hence hairyness is of more importance than spinyness in specific dist.). The Persicaria becoming hairy when removed from moist places is natural: hairs are believed to be provided as hygrometric appendages, to modify respiration & transpiration, water plants don’t want them. It is facts such as the Irish yew presents that afford fair grounds for argument on such a topic. 5
Quoting instances by tens or hundreds of variation in individual species is nothing new,6 few have an idea of the labor required to establish or destroy a species of a mundane genus. You have a Senebiera from Tres Montes, its capsules are much larger than the common S. pinnatifida, but that is so universally diffused a plant & so variable in the size of its leaves that at first sight no one would be inclined to grant specific dignity to the Tres Montes plant from the capsules. It struck me to put this subject to a Geographical test; the result is, that the S. pinnatifida is probably a native of the Plate alone, whence it has spread by ships over all East & W. America, all West Europe near the coast, in fact both shores of the Atlantic from Britain to the Cape & from Patagonia to Canada, wherever ships touch & cultiv. ensues, & on E. from Valp to California, wherever ships go, but through many hundreds of specimens there is no variation whatever in the size of the pods. & I therefore conclude that the Tres Montes plant is the W. coast representative of the E. coast plant.
Now though D. C. had hinted that S. pinn. was an American plant, he did not define its limits & retained two or three identical plants as different species which came from out of the ways localities:7 to define its limits I had not only to consult all floras where it was described, but all where it was not, for such a mundane plant creeps into every flora. My troubles did not end here, for I had no Valparaiso Senebiera & Bertero has an undescribed one from that port, which is alluded to as S. diffusa, Bert. mss. I naturally concluded your’s was this, but thought I would go to Brit. Mus to confirm it for fear of accident, but Bertero’s was genuine pinnatifida, he gave it a new name taking for granted it was a new species. So as S. pinnat. does not at Valp. vary into big pods, I am more persuaded that yours is a rep. species of W. coast of Am.—8 That Neutral territory of rep. species you ask about is just what I want to work out but it needs great materials
Ever yours most truly | J D Hooker
The most experienced botanists argue for the "validity of species in nature". Against taxonomic "splitters".
CD’s Cape Tres Montes plants.
Please cite as
Darwin Correspondence Project, “Letter no. 914,” accessed on 14 February 2016, http://www.darwinproject.ac.uk/DCP-LETT-914