I thank you for so kindly taking the trouble of writing to me, on naturalised plants.2 I did not know of or had forgotten the clover case. How I wish I knew what plants the Clover took the place of; but that would require more accurate knowledge of any one piece of ground than I suppose any one has. In the case of trees, being so long-lived, I sh^d. think it would be extremely difficult to distinguish between true & new spreading of a species, & a rotation of crop.

With respect to your idea of plants travelling west, I was much struck by a remark of yours in the penultimate Linnean Journal on the spreading of plants from America near Behring St^s. 3 Do you not consider so many more seeds & plants being taken from Europe to America, than in a reverse direction, would go some way to account for comparative fewness of naturalised American plants here. Though I think one might wildly speculate on European weeds having become well fitted for cultivated land, during thousands of years of culture, whereas cultivated land would be a new home for native American weeds, & they would not consequently be able to beat their European rivals when put in contest with them on cultivated land. Here is a bit of wild theory!

But I did not sit down intending to scribble thus; but to beg a favour of you: I gave Hooker a list of species of Silene, on which Gærtner has experimentised in crossing:4 now I want extremely to be permitted to say that such & such are believed by M^r Bentham to be true species, & such & such to be only varieties.5 Unfortunately & stupidly Gærtner does not append authors’ names to the species.—

Thank you heartily for what you say about my Book; but you will be greatly disappointed; it will be grievously too hypothetical. It will very likely be of no other service than collocating some facts; though I myself think I see my way approximately on the origin of species. But, alas, how frequent, how almost universal it is in an author to persuade himself of the truth of his own dogmas. My only hope is that I certainly see very many difficulties of gigantic stature.

Believe me | My dear Sir | Yours very sincerely | C. Darwin

If you can remember any cases of one introduced species beating out or prevailing over another, I sh^d be most thankful to hear it.—6

I believe the common Corn Poppy has been seen indigenous in Sicily; I sh^d. like to know whether you suppose that seedlings of this wild plant, would stand a contest with our own Poppy: I sh^d. almost expect that our Poppies were in some degree acclimatised & accustomed to our corn-fields. If this could be shown to be so in this & other cases I think we could understand why many not-trained American plants would not succeed in our agragrian habitats.