TO J.D.HOOKER.

Down, March 19th [1845].
...I was very glad to hear Humboldt's views on migrations and double creations.

It is very presumptuous, but I feel sure that though one cannot prove extensive migration, the leading considerations, proper to the subject, are omitted, and I will venture to say even by Humboldt.
I should like some time to put the case, like a lawyer, for your consideration, in the point of view under which, I think, it ought to be viewed.

The conclusion which I come to is, that we cannot pretend, with our present knowledge, to put any limit to the possible, and even probable, migration of plants.

If you can show that many of the Fuegian plants, common to Europe, are found in intermediate points, it will be a grand argument in favour of the actuality of migration; but not finding them will not, in my eyes, much diminish the probability of their having thus migrated.