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Overworked as you are, I dare say you will say that I am an odious plague;but here is another suggestion! I was led by one of my wild speculations to conclude (though it has nothing to do with geographical distribution, yet it has with your statistics) that trees would have a strong tendency to have flowers with dioecious, monoecious or polygamous structure. Seeing that this seemed so in Persoon, I took one little British Flora, and discriminating trees from bushes according to Loudon, I have found that the result was in species, genera and families, as I anticipated. So I sent my notions to Hooker to ask him to tabulate the New Zealand Flora for this end, and he thought my result sufficiently curious, to do so; and the accordance with Britain is very striking, and the more so, as he made three classes of trees, bushes, and herbaceous plants. (He says further he shall work the Tasmanian Flora on the same principle.) The bushes hold an intermediate position between the other two classes. It seems to me a curious relation in itself, and is very much so, if my theory and explanation are correct. (See 'Origin,' Edition i., page 100.)With hearty thanks, your most troublesome friend, C. DARWIN.

CHARLES DARWIN TO J.D. HOOKER.

Down, April 12th [1857].

My dear Hooker, Your letter has pleased me much, for I never can get it out of my head, that I take unfair advantage of your kindness, as I receive all and give nothing. What a splendid discussion you could write on the whole subject of variation! The cases discussed in your last note are valuable to me (though odious and damnable), as showing how profoundly ignorant we are on the causes of variation. I shall just allude to these cases, as a sort of sub-division of polymorphism a little more definite, I fancy, than the variation of, for instance, the Rubi, and equally or more perplexing.

I have just been putting my notes together on variations APPARENTLY due to the immediate and direct action of external causes; and I have been struck with one result. The most firm sticklers for independent creation admit, that the fur of the SAME species is thinner towards the south of the range of the same species than to the north--that the SAME shells are brighter-coloured to the south than north; that the same [shell] is paler-coloured in deep water--that insects are smaller and darker on mountains--more livid and testaceous near sea--that plants are smaller and more hairy and with brighter flowers on mountains: now in all such, and other cases, distinct species in the two zones follow the same rule, which seems to me to be most simply explained by species, being only strongly marked varieties, and therefore following the same laws as recognised and admitted varieties. Imention all this on account of the variation of plants in ascending mountains; I have quoted the foregoing remark only generally with no examples, for I add, there is so much doubt and dispute what to call varieties; but yet I have stumbled on so many casual remarks on VARIETIESof plants on mountains being so characterised, that I presume there is some truth in it. What think you? Do you believe there is ANY tendency in VARIETIES, as GENERALLY so-called, of plants to become more hairy and with proportionally larger and brighter-coloured flowers in ascending a mountain?

I have been interested in my "weed garden," of 3 x 2 feet square: I mark each seedling as it appears, and I am astonished at the number that come up, and still more at the number killed by slugs, etc. Already 59 have been so killed; I expected a good many, but I had fancied that this was a less potent check than it seems to be, and I attributed almost exclusively to mere choking, the destruction of the seedlings. Grass-seedlings seem to suffer much less than exogens...

CHARLES DARWIN TO J.D. HOOKER.

Moor Park, Farnham [April (?) 1857].

My dear Hooker, Your letter has been forwarded to me here, where I am undergoing hydropathy for a fortnight, having been here a week, and having already received an amount of good which is quite incredible to myself and quite unaccountable.

I can walk and eat like a hearty Christian, and even my nights are good. Icannot in the least understand how hydropathy can act as it certainly does on me. It dulls one's brain splendidly; I have not thought about a single species of any kind since leaving home. Your note has taken me aback; Ithought the hairiness, etc., of Alpine SPECIES was generally admitted; I am sure I have seen it alluded to a score of times. Falconer was haranguing on it the other day to me. Meyen or Gay, or some such fellow (whom you would despise), I remember, makes some remark on Chilian Cordillera plants.

Wimmer has written a little book on the same lines, and on VARIETIES being so characterised in the Alps. But after writing to you, I confess I was staggered by finding one man (Moquin-Tandon, I think) saying that Alpine flowers are strongly inclined to be white, and Linnaeus saying that cold makes plants APETALOUS, even the same species! Are Arctic plants often apetalous? My general belief from my compiling work is quite to agree with what you say about the little direct influence of climate; and I have just alluded to the hairiness of Alpine plants as an EXCEPTION. The odoriferousness would be a good case for me if I knew of VARIETIES being more odoriferous in dry habitats.

I fear that I have looked at the hairiness of Alpine plants as so generally acknowledged that I have not marked passages, so as at all to see what kind of evidence authors advance. I must confess, the other day, when I asked Falconer, whether he knew of INDIVIDUAL plants losing or acquiring hairiness when transported, he did not. But now THIS SECOND, my memory flashes on me, and I am certain I have somewhere got marked a case of hairy plants from the Pyrenees losing hairs when cultivated at Montpellier.