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Darwin Correspondence Project

To J. S. Burdon Sanderson   25 July 1873

Down, | Beckenham, Kent.

July 25 1873

My dear Dr Sanderson

I shd like to tell you a little about my recent work with Drosera, to shew that I have profited by yr suggestions, & to ask a question or two.1

(1) It is really beautiful how quickly & well Drosera & Dionæa dissolve little cubes of albumen & gelatine. I kept the same sized cubes on wet moss for comparison. When you were here I forgot that I had tried gelatine, but albumen is far better for watching its dissolution & absorption2

Frankland has told me how to test in a rough way for pepsine; & in the autumn he will discover what acid the digestive juice contains.3

(2) A decoction of cabbage leaves & green peas causes as much inflection as an infusion of raw meat: a decoction of grass is less powerful. Though I hear that the chemists try to precipitate all albumen from the ext. of Belladonna, I think they must fail, as the ext. causes inflection, whereas a new lot of Atropine, as well as the Valerianate, produce no effect.4

(3) I have been trying a good many experiments with heated water. I got a new chemical therm. & placed the long bulb obliquely, not touching the bottom of the vessel with 3 oz of water & I immersed & moved the leaves about. A temp. of from 100o to 125o Fahr. causes strong inflection within 10 minutes. A temp. of from 80o to 100o causes some inflection, but after a much longer time.

At 130o there is never any inflection, but the leaf is not killed as is proved by subsequent inflection when placed in a Sol. of Carb. of Ammonia; & by re-expansion when afterwards placed in pure water. The vitality of the leaves is also shewn by the aggregation of the protoplasm when the leaves are given Carb. of Amm. All this holds good until the leaves are heated up to or above 145o. Between 145o & 151o there is a remarkable change; the glands become as white as porcelain, & there is no inflection, nor aggregation of protoplasm when they are immersed in Carb. of Amm. Should you not call the following case one of heat rigor? Two leaves were heated to 130o; & had every tentacle closely inflected; one was taken out & placed in cold water, & it re-expanded; the other was heated to 145o, & had not the least power of re-expansion. Is not this latter case heat rigor? If you can inform me, I shd very much like to hear, at what temp. cold-blooded & invertebrate animals are killed.5

(4.) I must tell you my final result, of which I am sure, of the sensitiveness of Drosera. I made a solution of one pt of Phosphate of Amm. by weight to 218, 750 of water: of this sol.— I gave so much that a leaf got 18000th of a grain of the phosphate. I then counted the glands & each cd. have got only 1/1,552,000 of a grain; this being absorbed by the glands, sufficed to cause the tentacles bearing these glands to bend thro’ an angle of 180o. Such sensitiveness requires hot weather & carefully selected young, yet mature leaves. It strikes me as a wonderful fact—

I must add that I took every precaution, by trying numerous leaves at the same time in the sol. & in the same water which was used for making the sol—6

(5) If you can persuade yr friend to try the effects of C. of Amm. on the aggregation of the white blood corpuscles, I shd very much like to hear the result.7

I hope this letter will not have wearied you. Believe me | yours very sincerely | Charles Darwin


The letter containing Burdon Sanderson’s suggestions has not been found.
CD described experiments with albumen and gelatine in Insectivorous plants, pp. 92–8 and 110–12; see also letter to Edward Frankland, 12 July 1873. Emma Darwin’s diary (DAR 242) records that Burdon Sanderson visited Down on 4 July 1873.
CD described these experiments in Insectivorous plants, pp. 82–4 and 204. Atropine is a constituent of Atropa belladonna (deadly nightshade); valerianate of atropine is produced by adding valerianic (isobutyric) acid to atropine. He wanted to determine whether it was albumin, rather than the nightshade poison (atropine), that affected the leaves of Drosera. For correspondence between CD and his chemist on the purity of belladonna extract, see Correspondence vol. 20, letters to W. W. Baxter, 2 [December 1872] and [after 4 December 1872], and letter from W. W. Baxter, 4 December 1872.
CD recorded these experiments in the chapter ‘The effects of heat on leaves’ in Insectivorous plants, pp. 66–75.
The experiments with phosphate of ammonia were described in Insectivorous plants, pp. 153–66.
The friend was William Osler (see letter from J. S. Burdon Sanderson, 28 July [1873] and n. 3).


Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 27 vols to date. Cambridge: Cambridge University Press. 1985–.

Insectivorous plants. By Charles Darwin. London: John Murray. 1875.


Describes his recent work on Drosera digestion of organic materials, e.g., albumen and gelatin. Edward Frankland has given CD a rough test for pepsin. Some plant extracts cause as much inflection as meat. Has found some reversible inflection with heat and perhaps some heat rigor. Has measured the extreme sensitivity of Drosera with very dilute solution of ammonium phosphate.

Please cite as

Darwin Correspondence Project, “Letter no. 8987,” accessed on 25 September 2021,

Also published in The Correspondence of Charles Darwin, vol. 21