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 analogous 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 MOSTcomplex. The bladders catch a multitude 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 Ifound on the roots near the surface, and down to a depth of two inches in the sand. They are as transparent as glass, 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 mass. 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, Imean 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 Ladyship'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 ladyship'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, Iwill 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 manuscript 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 publishing 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.]
