Life and Letters of Charles Darwin Volume II Part 61

CHARLES DARWIN TO J. BURDON SANDERSON. Down, July 25, 1873.

My dear Dr. Sanderson,

I should like to tell you a little about my recent work with Drosera, to show that I have profited by your suggestions, and to ask a question or two.

1. It is really beautiful how quickly and well Drosera and Dionaea dissolve little cubes of alb.u.men and gelatine. I kept the same sized cubes on wet moss for comparison. When you were here I forgot that I had tried gelatine, but alb.u.men is far better for watching its dissolution and absorption. Frankland has told me how to test in a rough way for pepsin; and in the autumn he will discover what acid the digestive juice contains.

2. A decoction of cabbage-leaves and green peas causes as much inflection as an infusion of raw meat; a decoction of gra.s.s is less powerful. Though I hear that the chemists try to precipitate all alb.u.men from the extract of belladonna, I think they must fail, as the extract causes inflection, whereas a new lot of atropine, as well as the valerianate [of atropine], produce no effect.

3. I have been trying a good many experiments with heated water... Should you not call the following case one of heat rigor? Two leaves were heated to 130 deg, and had every tentacle closely inflected; one was taken out and placed in cold water, and it re-expanded; the other was heated to 145 deg, and had not the least power of re-expansion. Is not this latter case heat rigor? If you can inform me, I should very much like to hear at what temperature cold-blooded and invertebrate animals are killed.

4. I must tell you my final result, of which I am sure, [as to] the sensitiveness of Drosera. I made a solution of one part of phosphate of ammonia by weight to 218,750 of water; of this solution I gave so much that a leaf got 1/8000 of a grain of the phosphate. I then counted the glands, and each could have got only 1/1552000 of a grain; this being absorbed by the glands, sufficed to cause the tentacles bearing these glands to bend through an angle of 180 deg. Such sensitiveness requires hot weather, and 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 solution and in the same water which was used for making the solution.

5. If you can persuade your friend to try the effects of carbonate of ammonia on the aggregation of the white blood corpuscles, I should very much like to hear the result.

I hope this letter will not have wearied you.

Believe me, yours very sincerely, CHARLES DARWIN.

CHARLES DARWIN TO W. THISELTON DYER. Down, 24 [December 1873?].

My dear Mr. Dyer,

I fear that you will think me a great bore, but I cannot resist telling you that I have just found out that the leaves of Pinguicula possess a beautifully adapted power of movement. Last night I put on a row of little flies near one edge of two YOUNGISH leaves; and after 14 hours these edges are beautifully folded over so as to clasp the flies, thus bringing the glands into contact with the upper surfaces of the flies, and they are now secreting copiously above and below the flies and no doubt absorbing. The acid secretion has run down the channelled edge and has collected in the spoon-shaped extremity, where no doubt the glands are absorbing the delicious soup. The leaf on one side looks just like the helix of a human ear, if you were to stuff flies within the fold.

Yours most sincerely,

CH. DARWIN.

CHARLES DARWIN TO ASA GRAY. Down, June 3 [1874].

... I am now hard at work getting my book on Drosera & Co. ready for the printers, but it will take some time, for I am always finding out new points to observe. I think you will be interested by my observations on the digestive process in Drosera; the secretion contains an acid of the acetic series, and some ferment closely a.n.a.logous to, but not identical with, pepsin; for I have been making a long series of comparative trials. No human being will believe what I shall publish about the smallness of the doses of phosphate of ammonia which act.

... I began reading the Madagascar squib (A description of a carnivorous plant supposed to subsist on human beings.) quite gravely, and when I found it stated that Felis and Bos inhabited Madagascar, I thought it was a false story, and did not perceive it was a hoax till I came to the woman...

CHARLES DARWIN TO F.C. DONDERS. (Professor Donders, the well-known physiologist of Utrecht.) Down, July 7, 1874.

My dear Professor Donders,

My son George writes to me that he has seen you, and that you have been very kind to him, for which I return to you my cordial thanks. He tells me on your authority, of a fact which interests me in the highest degree, and which I much wish to be allowed to quote. It relates to the action of one millionth of a grain of atropine on the eye. Now will you be so kind, whenever you can find a little leisure, to tell me whether you yourself have observed this fact, or believe it on good authority.

I also wish to know what proportion by weight the atropine bore to the water solution, and how much of the solution was applied to the eye. The reason why I am so anxious on this head is that it gives some support to certain facts repeatedly observed by me with respect to the action of phosphate of ammonia on Drosera. The 1/4000000 of a grain absorbed by a gland clearly makes the tentacle which bears this gland become inflected; and I am fully convinced that 1/20000000 of a grain of the crystallised salt (i.e. containing about one-third of its weight of water of crystallisation) does the same. Now I am quite unhappy at the thought of having to publish such a statement. It will be of great value to me to be able to give any a.n.a.logous facts in support. The case of Drosera is all the more interesting as the absorption of the salt or any other stimulant applied to the gland causes it to transmit a motor influence to the base of the tentacle which bears the gland.

Pray forgive me for troubling you, and do not trouble yourself to answer this until your health is fully re-established.

Pray believe me, Yours very sincerely, CHARLES DARWIN.

[During the summer of 1874 he was at work on the genus Utricularia, and he wrote (July 16th) to Sir J.D. Hooker giving some account of the progress of his work:--

"I am rather glad you have not been able to send Utricularia, for the common species has driven F. and me almost mad. The structure is MOST complex. The bladders catch a mult.i.tude of Entomostraca, and larvae of insects. The mechanism for capture is excellent. But there is much that we cannot understand. From what I have seen to-day, I strongly suspect that it is necrophagous, i.e. that it cannot digest, but absorbs decaying matter."

He was indebted to Lady Dorothy Nevill for specimens of the curious Utricularia montana, which is not aquatic like the European species, but grows among the moss and debris on the branches of trees. To this species the following letter refers:]

CHARLES DARWIN TO LADY DOROTHY NEVILL. Down September 18 [1874].

Dear Lady Dorothy Nevill,

I am so much obliged to you. I was so convinced that the bladders were with the leaves that I never thought of removing the moss, and this was very stupid of me. The great solid bladder-like swellings almost on the surface are wonderful objects, but are not the true bladders. These I found on the roots near the surface, and down to a depth of two inches in the sand. They are as transparent as gla.s.s, from 1/20 to 1/100 of an inch in size, and hollow. They have all the important points of structure of the bladders of the floating English species, and I felt confident I should find captured prey. And so I have to my delight in two bladders, with clear proof that they had absorbed food from the decaying ma.s.s. For Utricularia is a carrion-feeder, and not strictly carnivorous like Drosera.

The great solid bladder-like bodies, I believe, are reservoirs of water like a camel's stomach. As soon as I have made a few more observations, I mean to be so cruel as to give your plant no water, and observe whether the great bladders shrink and contain air instead of water; I shall then also wash all earth from all roots, and see whether there are true bladders for capturing subterranean insects down to the very bottom of the pot. Now shall you think me very greedy, if I say that supposing the species is not very precious, and you have several, will you give me one more plant, and if so, please to send it to "Orpington Station, S.E.R., to be forwarded by foot messenger."

I have hardly ever enjoyed a day more in my life than I have this day's work; and this I owe to your Ladys.h.i.+p's great kindness.

The seeds are very curious monsters; I fancy of some plant allied to Medicago, but I will show them to Dr. Hooker.

Your ladys.h.i.+p's very gratefully, CH. DARWIN.

CHARLES DARWIN TO J.D. HOOKER. Down, September 30, 1874.

My dear H.,

Your magnificent present of Aldrovanda has arrived quite safe. I have enjoyed greatly a good look at the shut leaves, one of which I cut open.

It is an aquatic Dionaea, which has acquired some structures identical with those of Utricularia!

If the leaves open and I can transfer them open under the microscope, I will try some experiments, for mortal man cannot resist the temptation.

If I cannot transfer, I will do nothing, for otherwise it would require hundreds of leaves.

You are a good man to give me such pleasure.

Yours affectionately, C. DARWIN.

[The ma.n.u.script of 'Insectivorous Plants' was finished in March 1875.

He seems to have been more than usually oppressed by the writing of this book, thus he wrote to Sir J.D. Hooker in February:--

"You ask about my book, and all that I can say is that I am ready to commit suicide; I thought it was decently written, but find so much wants rewriting, that it will not be ready to go to printers for two months, and will then make a confoundedly big book. Murray will say that it is no use publis.h.i.+ng in the middle of summer, so I do not know what will be the upshot; but I begin to think that every one who publishes a book is a fool."

The book was published on July 2nd, 1875, and 2700 copies were sold out of the edition of 3000.]

CHAPTER 2.XIV. -- THE 'POWER OF MOVEMENT IN PLANTS.'