Dear Darwin

I have delayed answering your letter till my return here, in the hopes that it might be possible to accept your kind invitation to meet Capt. Sulivan at Down. Two visitors however tie me by the leg, one of them our friend Harvey of Dublin, who I only see once a year: had it been otherwise I would have run down for the Sunday of next week, when I suppose, from your letter, Capt. S. will be with you.

Hopkirk reached me quite safe, now long ago, the work is curious as being one of the very few English ones devoted to the subject: unfortunately the author seems to have had no direct object in writing or very clear arrangement.¹

“Plants & soils” is a long subject, I am tolerably convinced now, from a little observation of my own, that the mechanical & not the chemical qualities of the soil are the important ones. There is I expect hardly any soil that does not contain enough of the inorganic elements that any plant wants, to support a growth of such plants. Still there are assemblages of limestone-plants, & the predilection of such for that rock in England remains to be explained. If it be granted that the Limestone (& chalk) are warmer soils (& all the information I can collect goes to prove it) than the Sandstones, then the solution will be easy, for I think I can show that the Southern extension of the Scotch plants in England is upon the Sandstones & the N. extension of continental species in Britain upon the Calc. rocks. There are hundreds of exceptions, but these comprehensive questions must not be worked by exceptions, which may prove to be only apparent when the leading facts are established. The black traps will help me; for their dry hot sunny slopes on the Clyde present us with plants confined on the Severn to the Mt: Limestone. Sir H.² wants the difficulty solved by examinations of the areas squared out on his Ordnance maps; I am not capable of generalizing from such a limited field of observation, though others doubtless are who are better skilled in making the most of small means; were I to follow the subject as I would like, I should examine the sites of the local British species on the continent..

Many thanks for mentioning Herberts paper, I have it in my eye all along, it is as you say a good deal to the purpose. Another year I should like much to work a little at your chalk & clay floras but have no idea of what a summer may bring forth: if Sir H. will not let me work the thing as any Botanist would advise, I should throw it up; though this I have never hinted to any one: but Sir. H. though a kind, good man, has no system of his own & cannot bear Forbes & my working with books.

How glad I shall be when your S. A. is done, you will then feel freer than you have for long. I know no greater pleasure than getting a tedious job out of hand when one has really been doing the best to it.

It was very stupid of me to say 2 square yds instead of 2 yd^s. square but it is a mistake I always make when not thinking. I have just been told of 27 mosses (not Hepatica) on one rock i.e. block of rock in Scotland & there are only some 300 sp. in Britain. Watson supposes that every county contains upwards of one half the whole British Flora.³

When such results of any comparisons between the representative species of the N. & S. hemispheres that my Flora will shew, shall be worked out, I shall probably publish them in the L. Soc. Trans. which will save me the labor of getting them through the press myself, even if any publisher w^d. undertake them, which is not likely.⁴ I have not seen Forbes since studying his paper & really do not know what to say when I do, for he will be sure to ask me about it, & most unfortunately he does not seem to know the Geographic Distrib. of the English Plants. I must confess to have taken his modification of Watson’s types of vegetation as correct, & this for granted, but I had occasion to look closely at them the other day & find his S.E Flora, numbered III., to be altogether a fallacy: all or almost all the 20 species on whose supposed presence he founds it, being as common or more in the W. or N as in the E. or S. & some of them not existing in the S.E. at all.! or if so as introduced species. I now see the cause for Watson’s being so peculiarly savage & offering me proof that all that is correct is mere plagiarism. I still however quite acquit Forbes of any intentional piracy, he has long & early understood & appreciated Watson’s views & has fancied that he has grounds for modifying them. I do all I can to appease W., but in vain, he threatens to denounce F. publicly & if he does I fear that it will read awkwardly for our friend. I need not ask you to say nothing of this, except you can offer some way or means of keeping these, almost the only 2 Philosophical Brit. Botanists, out of a broil, at which all the dirty species-mongers will chuckle.⁵

I will send you one of Watson’s works at once: you must judge it by what has been previously done, or even done up to this time, by any other Brit. Bot.; more than by its own intrinsic merits, which however are very high.

I have excluded all of Edmonstones plants that can have been from the Coast. A great developement of an organ in plants is often accompanied by a suppression of others E.G. Rafflesia, a staring xample: I should like to have the opportunity of applying S^t. Hilaires laws directly to the subject. I have heard of them.

Of Deiffenbach I know nothing whatever.

I do not intend to work much more for the Geol. Mus. this year, except at home, I have a great deal on hand.

I could not get to the Brit. Assoc. I wanted much to have got to Switzerland or Germany but could not. Two more Mediterranean Algæ have been found within these few months on the W. of Ireland.

Have you seen the new Cosmos?⁶ it is excellently well done & quite a different book to read— I will send or bring it you if you care. Should Capt. Sulivan stay over Sunday week with you, & it be entirely convenient for me to come, I w^d. try & get down, if only for a day, but do not see why I should not take my usual allowance at Down..

Ever most truly Yours | Jos D Hooker.