My dear Sir

I have taken up your list of British plts with subspecies or varieties several times during the week, & still with the same idea arising;—namely, that I am not prepared to go seriatim through it in the manner, & with the brevity, you desired.—² I do not think any botanist can. And thus, I fear, the only result of my beginning to write notes on your list, is, that the list is defaced & spoilt for any other use.

In writing the final volume of my Cybele Britannica, I find myself unable to carry out the ideas or inquiries originally intended.³ And why?— Mainly, because the limits of species are so uncertain in nature,—so dissimilar in books. Add to this, the extreme inequality in the Structural value of groups designated by the same abstract term (ex. gr. Orders). The result is, I can only group & compare details,—not condense them into real generalisations.

This leads me to devote many pages to my own notions about species & classifications,—rather irrelevant in a book on local botany;—& perhaps somewhat limping over that same ground which will be better trod by yourself.⁴ I cannot find the proof of species being definite & immutable, whatever they may seem to be at any one time & spot.—

Sincerely | Hewett C^l. Watson Charles Darwin | Esq