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Darwin Correspondence Project

To Edward Frankland   29 September 1873

Down, | Beckenham, Kent.

Sep 29. 1873

My dear Sir

I herewith send the washings of 445 leaves (many of them small & poor) in about 8 oz of your distilled water, with 20 grains of yr Carb. of Soda; but much of the solution has been lost in taking out the leaves.1 I have followed all the precautions suggested by you, but then I have found it impossible to prevent some minute insects, completely hidden amongst the tentacles, being included; so that there will, I presume, be traces of Chloride of Sodium. Secondly, I find that the juice of the footstalk & leaf itself is strongly acid, judging by litmus paper; & it was impossible to keep the cut off footstalk entirely out of the solution. So that there will be some acid from this source, independently of that secreted by the glands; but it seems probable that both are the same acid. There seems to be a good deal of acid secreted by the glands, as the bits of fibrin produced little bubbles in the sol. of Soda.2 I shall be intensely curious to know what the acid is.

I have sent all the leaves wrapped up in tin-foil after they had been washed in the Solution; & if it is not a very difficult job, could you get any of your pupils to ascertain what acid is in the leaves themselves. I would gladly pay for this work if you cd persuade any one to undertake it. In this case the leaves I suppose ought to be washed in order to remove any of the secretion, & then crushed.

I have put the solution into 2 bottles, as I had not a stopper-bottle large enough to hold all;— but all is of the same nature.

I am very much obliged for the large bottle of pure water, & had no idea how difficult it was to get it pure: it will be of especial use to me in a distinct little investigation that I am undertaking. I have written to Dr. Odling to thank him.3

Thank you much for your offer of Mucin &c; but Dr Moore is making this substance & every thing for me which I require, except Ptyalin,4 & this he tells me is very difficult to procure, on account of the difficulty of getting enough Saliva, tho’ I shd want only about 1 or 2 grains.

With sincere thanks | Yours very faithfully | Ch. Darwin

There are thousands of the glands in the soln. & you will see how minute they are & I shall be surprised if they have secreted acid enough to neutralise more than 1 gr of the Soda.—


Frankland had offered to test the washings of Drosera (sundew) leaves for the presence of hydrochloric acid (see letter from Edward Frankland, 22 September 1873).
Frankland had recommended that CD add carbonate of soda (sodium carbonate) to the leaves to try to increase the output of acid secretion by the plant (see letter from Edward Frankland, 22 September 1873).
CD’s letter to William Odling has not been found.
Ptyalin is found in saliva; it catalyses starch. No letter from Samuel William Moore mentioning ptyalin has been found.


Is sending washings of 445 leaves in EF’s distilled water with 20 grains of carbonate of soda. Details of the difficulties and complications involved.

Letter details

Letter no.
Charles Robert Darwin
Edward Frankland
Sent from
Source of text
The John Rylands Library, The University of Manchester
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 9077A,” accessed on 21 September 2021,

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