Muller's (343/3. Ferdinand
Muller.) letter to me, in which he says: "In the WILDERNESSES of
Australia some European perennials are "advancing in sure progress,"
"not to be arrested," etc. He gives as instances (so I suppose there
are other cases) eleven species, viz., 3. Rumex, Poterium sanguisorba,
Potentilla anserina, Medicago sativa, Taraxacum officinale, Marrubium
vulgare, Plantago lanceolata, P. major, Lolium perenne. All these are
seeding freely. Now I remember, years and years ago, your discussing
with me how curiously easily plants get naturalised on uninhabited
islands, if ships even touch there. I remember we discussed packages
being opened with old hay or straw, etc. Now think of hides and wool
(and wool exported largely over Europe), and plants introduced, and
samples of corn; and I must think that if Australia had been the old
country, and Europe had been the Botany Bay, very few, very much
fewer, Australian plants would have run wild in Europe than have now in
Australia.

The case seems to me much stronger between La Plata and Spain.

Nevertheless, I will put in my one sentence on this head, illustrating
the greater migration during Glacial period from north to south than
reversely, very humbly and cautiously. (343/4. "Origin of Species,"
Edition I., page 379. Darwin refers to the facts given by Hooker and De
Candolle showing a stronger migratory flow from north to south than in
the opposite direction. Darwin accounts for this by the northern plants
having been long subject to severe competition in their northern homes,
and having acquired a greater "dominating power" than the southern
forms. "Just in the same manner as we see at the present day that very
many European productions cover the ground in La Plata, and in a lesser
degree in Australia, and have to a certain extent beaten the natives;
whereas extremely few southern forms have become naturalised in any part
of Europe, though hides, wool, and other objects likely to carry seeds
have been largely imported during the last two or three centuries from
La Plata, and during the last thirty or forty years from Australia.')

I am very glad to hear you are making good progress with your Australian
Introduction. I am, thank God, more than half through my chapter on
geographical distribution, and have done the abstract of the Glacial
part...

LETTER 344. TO J.D. HOOKER. Down, March 30th, 1859.

Many thanks for your agreeable note. Please keep the geog