Dear M^r. Darwin,

I am much ashamed at having allowed so long a time to elapse, without acknowledgement of your kindness in sending me a copy of the “Forms of Flowers”.¹ The fact is, I thought I would read the book before writing; and fondly imagined that I should find time to do this straight off. But what with one and another interruption I have even now only imperfectly read it. I can however no longer delay expressing my hearty thanks to you, and offering my congratulations on this new block that you have added to the huge pyramid you are constructing to your glory. I owe you also minor thanks for having told me of Kerner’s book on “Unbidden guests”.² I took it with me to Italy this spring and it did much to make a wet holiday less unbearable. I fancy that there is still much to be made out as to the hairiness of plants, and that it has more to do with preventing insects crawling up plants, than Kerner would seem to allow.³ I noticed that on some plants, where the hairs were not close or long enough to cause much mechanical hindrance, ants, though they moved about readily at first, seemed soon to suffer irritation, stopping and rubbing themselves as though stung. It is strange also, that in no few plants—e.g. Bugle and Veronica Chamædrys⁴—the hairs only grow on two of the four sides of the stem, changing at each node, and being so placed as always to block up the path upwards between each pair of leaves. Again it is a curious thing that no Water plant, so far as I can make out, is ever hairy. Of the many plants specifically distinguished as “hirsuta” not one seems to be a water plant. Most or all of the Veronicas that grow on dry soil are hairy more or less; but all the species that grow in the water are perfectly smooth. Why is this? I fancy that the explanation is, that water plants are already protected by the water from creeping insects and therefore require no hairs.

But it is possible that the explanation is to be found in some of the other uses of hairs enumerated by Kerner in the note to p. 38.⁵ One such use for instance is to prevent evaporation, and to keep the plant duly moistened by condensing dew; and this of course is not required by water plants.

Pray forgive me for venturing to trouble you with these crude and rudimentary speculations. If there be one more valuable lesson than another in your last book it is that one has no right to have any opinion at all upon such a question, without having first made a series of patiently conducted and well devised experiments.

Again let me express my thanks to you, and with every good wish | Believe me | Y^rs. sincerely | W. Ogle.