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Letter 11586

Darwin, C. R. to Darwin, Francis

2 July [1878]


Suggests FD call on Carl Semper.

Inquires about Porlieria: Do the leaves shut to check evaporation? Does it appear silver under water?

Explains how he thinks the pulvinus acts; wishes FD would investigate the point.


Down, | Beckenham, Kent. | Railway Station | Orpington. S.E.R.

July 2d

My dear F.

Murie has written to me & you, asking me if you were away to look over your revise, which I have done & found nothing to correct & no criticism to make to you, except that one or two sentences might have been clearer. The whole strikes me as excellent & conclusive.— The revise is marked “25 copies”: had you not better get more?—

I have sent cheque to a repeated bill from Griffin for 2.10.10— A thermometer has come from Kew, for which I have also paid,— I think 1.11.0.— There is a “certificate” with the thermometer.—

I will now go through your letter, but first will say that Bernard seems quite well, though temper not quite so placid as formerly. He has just started very happy & eager in “boobo” with Miss DorcyQQQQ & Bessy to the Station.

I think you certainly had better call on Semper; you can say that I asked you to do so to give my very kind remembrances. You know that he has lately returned from America—has travelled much in Philippines & Malay Arch.—has worked on same subjects as Balfour—is a first-rate man, & I liked him, but he is said to have bad temper & to think that everyone is depreciating him.— He dedicated a magnificent essay to me on eyes of a Mollusc,— Onchidium.—

I have written to Kew about Porliera: do the leaves look like silver under water? Can they shut up to check evaporation; something of this kind occurs (Duval-Jouve) with certain grapes: you could try (if you could get permission) by enclosing small branch in well wetted bottle with wet sponge.—

I am glad to hear that Sachs tries “fools experiments”.

Do what you think fit about the 10£ Telescope, & any other instrument; only do not waste money, as you know your honoured father hates this.

I go on maundering about the pulvinus, cushion or gland whichever you call it, & from what I have seen roughly in the petioles of the Cotyledons of oxalis, I conclude that a pulvinus must be developed from ordinary cells, which secrete water into the inter-cellular spaces on the concave side of a bending organ; & that a pulvinus is developed only when the bending has to be continued for a period after growth has ceased or nearly ceased.

The cotyledon of Oats bending towards light would, I think, do for observation, & I much wish that you wd. try either there, or here whether by cutting thin sections about 110th^. of inch above the soil of 2 or 3 cots:, you could measure under high power the diameter of the cells, & observe whether their diameter is the same all round. If you can ascertain their average diameter, then cut sections on the most bent part, at same height above soil as before, & see if cells on convave side of the stem where bent through heliotropism (or apogeotropism) are smaller than those on convex side. I cannot remember whether such observations have been made, but I think that they are worth making. If there is no such action, as I imagine how the deuce can a pulvinus be developed in all sorts of Families?

I am trying a slight modification of your dodge; & putting night-light under large bell-glass, standing on little wooden bricks to let some air come in, & I have succeeded in keepin jar of water for many hours between 75f0 & 80f0 F;

I have thanked Murie & returned revise.

DAR 211: 32


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