Lxviii MEMOIR. 
Dr. J. D. Hooker to H. W. Bates. 
“ KEw, Sunday. 
‘*My DEAR BATES, 
‘‘T am extremely glad to hear that Gray has come round; he is 
really a candid sort of man in his way, but a strange compound. 
‘‘T am delighted to hear that you are going to write on the geographical 
relations of species and varieties, upon which subject I know that you have a 
great deal of novel as well as pregnant matter that wants embodiment.”’ 
(Then follows advice as to publication of the paper in the Linnean 
Society’s Journal, as better insuring the attention of experts.) 
‘‘ Now for your questions. I think Wallace is so far right that in so far 
as the Arctic flora and regions are concerned, plants afford overwhelming 
evidence of distribution being effected mainly by geological change (including 
therein climatic change). The data are so good, the dispersion of forms 
over mountain areas so uniform, the contrast between American types and 
Scandinavian types so vivid, and the relations between continental, insular, 
and enznsudar floras so consonant to theory, that granting a glacial period 
the rest must follow on a proper tabulation of the floras. I should like to go 
over that essay with you with a map, and I think I could convince you that 
the single fact of Greenland being a peninsula, its necessary consequences or 
distributions are almost proofs of all the rest. 
“‘TJ.—I still think that, as a rule, the best marked varieties occur on the 
confines. I find it, I think, remarkably instanced in a paper J] am now 
working out on the relations of the temperate flora of Cameroons Mountains, 
in the Bight of Benin. Here Cape types find their extreme north limit, 
Abyssinian their west limit, and Scandinavian ones their south limit; and 
there are quite a number of forms of each which I really do not know 
whether to call species or varieties. On the other hand, no doubt many 
species present more varieties toward their focus than toward their circum- 
ference, and then again the subject presents itself under two aspects, 
thus : The common ivy presents four or five extremely dissimilar forms in 
Europe (its focus), but extending to its west extreme we have the Irish ivy, 
and to the east we have a very curious Himalayan form—certainly these two 
last differ more widely from one another than do any of the four European 
coincident varieties. There is nothing in all this against as great, or greater 
variations occurring within the focus. Again, as a rule, lowland plants and 
insects assume different forms on Alps; what is this but their varying most 
at this (upward) verge of their distribution? The fact of its being granted 
as a general rule that insects and plants do thus vary at heights, is assuming 
that they do not vary so much below. 
“‘ The question of varieties on islands opens a wide field, which I should 
extremely like to talk over with you afrofos of Darwin’s remark (which he 
and I are now corresponding about) that the absence of struggle in islands 
should tend to perpetuate original forms there. As to my own share in the 
origination of the doctrine of distribution by geological, etc., change, I 
cannot take the credit of it, as E. Forbes published before me, and his paper 
on the geological connection of the existing flora and fauna of the British 
Islands is the first essay on the subject known to me. I had, in the Antarctic 
