"Your note has pleased me much--for I did not expect that you would have had time to read _any_ of it. Read the last chapter, and you will know the whole result, but without the evidence. The case, however, of radicles bending after exposure for an hour to geotropism, with their tips (or brains) cut off is, I think worth your reading (bottom of p.
525); it astounded me. But I will bother you no more about my book. The sensitiveness of seedlings to light is marvellous."
To another friend, Mr. Thiselton Dyer, he wrote (November 28, 1880):
"Very many thanks for your most kind note, but you think too highly of our work, not but what this is very pleasant.... Many of the Germans are very contemptuous about making out the use of organs; but they may sneer the souls out of their bodies, and I for one shall think it the most interesting part of Natural History. Indeed you are greatly mistaken if you doubt for one moment on the very great value of your constant and most kind a.s.sistance to us."
The book was widely reviewed, and excited much interest among the general public. The following letter refers to a leading article in the _Times_, November 20, 1880:--
_C. D. to Mrs. Haliburton._[294] Down, November 22, 1880.
MY DEAR SARAH,--You see how audaciously I begin; but I have always loved and shall ever love this name. Your letter has done more than please me, for its kindness has touched my heart. I often think of old days and of the delight of my visits to Woodhouse, and of the deep debt of grat.i.tude which I owe to your father. It was very good of you to write. I had quite forgotten my old ambition about the Shrewsbury newspaper;[295] but I remember the pride which I felt when I saw in a book about beetles the impressive words "captured by C. Darwin." Captured sounded so grand compared with caught. This seemed to me glory enough for any man! I do not know in the least what made the _Times_ glorify me, for it has sometimes pitched into me ferociously.
I should very much like to see you again, but you would find a visit here very dull, for we feel very old and have no amus.e.m.e.nt, and lead a solitary life. But we intend in a few weeks to spend a few days in London, and then if you have anything else to do in London, you would perhaps come and lunch with us.
Believe me, my dear Sarah, Yours gratefully and affectionately.
The following letter was called forth by the publication of a volume devoted to the criticism of the _Power of Movement in Plants_ by an accomplished botanist, Dr. Julius Wiesner, Professor of Botany in the University of Vienna:
_C. D. to Julius Wiesner._ Down, October 25th, 1881.
MY DEAR SIR,--I have now finished your book,[296] and have understood the whole except a very few pa.s.sages. In the first place, let me thank you cordially for the manner in which you have everywhere treated me.
You have shown how a man may differ from another in the most decided manner, and yet express his difference with the most perfect courtesy.
Not a few English and German naturalists might learn a useful lesson from your example; for the coa.r.s.e language often used by scientific men towards each other does no good, and only degrades science.
I have been profoundly interested by your book, and some of your experiments are so beautiful, that I actually felt pleasure while being vivisected. It would take up too much s.p.a.ce to discuss all the important topics in your book. I fear that you have quite upset the interpretation which I have given of the effects of cutting off the tips of horizontally extended roots, and of those laterally exposed to moisture; but I cannot persuade myself that the horizontal position of lateral branches and roots is due simply to their lessened power of growth. Nor when I think of my experiments with the cotyledons of _Phalaris_, can I give up the belief of the transmission of some stimulus due to light from the upper to the lower part. At p. 60 you have misunderstood my meaning, when you say that I believe that the effects from light are transmitted to a part which is not itself heliotropic. I never considered whether or not the short part beneath the ground was heliotropic; but I believe that with young seedlings the part which bends _near_, but _above_ the ground is heliotropic, and I believe so from this part bending only moderately when the light is oblique, and bending rectangularly when the light is horizontal. Nevertheless the bending of this lower part, as I conclude from my experiments with opaque caps, is influenced by the action of light on the upper part. My opinion, however, on the above and many other points, signifies very little, for I have no doubt that your book will convince most botanists that I am wrong in all the points on which we differ.
Independently of the question of transmission, my mind is so full of facts leading me to believe that light, gravity, &c., act not in a direct manner on growth, but as stimuli, that I am quite unable to modify my judgment on this head. I could not understand the pa.s.sage at p. 78, until I consulted my son George, who is a mathematician. He supposes that your objection is founded on the diffused light from the lamp illuminating both sides of the object, and not being reduced, with increasing distance in the same ratio as the direct light; but he doubts whether this _necessary_ correction will account for the very little difference in the heliotropic curvature of the plants in the successive pots.
With respect to the sensitiveness of the tips of roots to contact, I cannot admit your view until it is proved that I am in error about bits of card attached by liquid gum causing movement; whereas no movement was caused if the card remained separated from the tip by a layer of the liquid gum. The fact also of thicker and thinner bits of card attached on opposite sides of the same root by sh.e.l.lac, causing movement in one direction, has to be explained. You often speak of the tip having been injured; but externally there was no sign of injury: and when the tip was plainly injured, the extreme part became curved _towards_ the injured side. I can no more believe that the tip was injured by the bits of card, at least when attached by gum-water, than that the glands of Drosera are injured by a particle of thread or hair placed on it, or that the human tongue is so when it feels any such object.
About the most important subject in my book, namely circ.u.mnutation, I can only say that I feel utterly bewildered at the difference in our conclusions; but I could not fully understand some parts which my son Francis will be able to translate to me when he returns home. The greater part of your book is beautifully clear.
Finally, I wish that I had enough strength and spirit to commence a fresh set of experiments, and publish the results, with a full recantation of my errors when convinced of them; but I am too old for such an undertaking, nor do I suppose that I shall be able to do much, or any more, original work. I imagine that I see one possible source of error in your beautiful experiment of a plant rotating and exposed to a lateral light.
With high respect, and with sincere thanks for the kind manner in which you have treated me and my mistakes, I remain,
My dear Sir, yours sincerely.
_Insectivorous Plants._
In the summer of 1860 he was staying at the house of his sister-in-law, Miss Wedgwood, in Ashdown Forest whence he wrote (July 29, 1860), to Sir Joseph Hooker:--
"Latterly I have done nothing here; but at first I amused myself with a few observations on the insect-catching power of Drosera:[297] and I must consult you some time whether my "twaddle" is worth communicating to the Linnean Society."
In August he wrote to the same friend:--
"I will gratefully send my notes on Drosera when copied by my copier: the subject amused me when I had nothing to do."
He has described in the _Autobiography_ (p. 47), the general nature of these early experiments. He noticed insects sticking to the leaves, and finding that flies, &c., placed on the adhesive glands, were held fast and embraced, he suspected that the captured prey was digested and absorbed by the leaves. He therefore tried the effect on the leaves of various nitrogenous fluids--with results which, as far as they went, verified his surmise. In September, 1860, he wrote to Dr. Gray:--
"I have been infinitely amused by working at Drosera: the movements are really curious; and the manner in which the leaves detect certain nitrogenous compounds is marvellous. You will laugh; but it is, at present, my full belief (after endless experiments) that they detect (and move in consequence of) the 1/2880 part of a single grain of nitrate of ammonia; but the muriate and sulphate of ammonia bother their chemical skill, and they cannot make anything of the nitrogen in these salts!"
Later in the autumn he was again obliged to leave home for Eastbourne, where he continued his work on Drosera.
On his return home he wrote to Lyell (November 1860):--
"I will and must finish my Drosera MS., which will take me a week, for, at the present moment, I care more about Drosera than the origin of all the species in the world. But I will not publish on Drosera till next year, for I am frightened and astounded at my results. I declare it is a certain fact, that one organ is so sensitive to touch, that a weight seventy-eight-times less than that, viz., 1/1000 of a grain, which will move the best chemical balance, suffices to cause a conspicuous movement. Is it not curious that a plant should be far more sensitive to the touch than any nerve in the human body? Yet I am perfectly sure that this is true. When I am on my hobby-horse, I never can resist telling my friends how well my hobby goes, so you must forgive the rider."
The work was continued, as a holiday task, at Bournemouth, where he stayed during the autumn of 1862.
A long break now ensued in his work on insectivorous plants, and it was not till 1872 that the subject seriously occupied him again. A pa.s.sage in a letter to Dr. Asa Gray, written in 1863 or 1864, shows, however, that the question was not altogether absent from his mind in the interim:--
"Depend on it you are unjust on the merits of my beloved Drosera; it is a wonderful plant, or rather a most sagacious animal. I will stick up for Drosera to the day of my death. Heaven knows whether I shall ever publish my pile of experiments on it."
He notes in his diary that the last proof of the _Expression of the Emotions_ was finished on August 22, 1872, and that he began to work on Drosera on the following day.
_C. D. to Asa Gray_ [Sevenoaks], October 22 [1872].
... I have worked pretty hard for four or five weeks on Drosera, and then broke down; so that we took a house near Sevenoaks for three weeks (where I now am) to get complete rest. I have very little power of working now, and must put off the rest of the work on Drosera till next spring, as my plants are dying. It is an endless subject, and I must cut it short, and for this reason shall not do much on Dionaea. The point which has interested me most is tracing the _nerves_! which follow the vascular bundles. By a p.r.i.c.k with a sharp lancet at a certain point, I can paralyse one-half the leaf, so that a stimulus to the other half causes no movement. It is just like dividing the spinal marrow of a frog:--no stimulus can be sent from the brain or anterior part of the spine to the hind legs: but if these latter are stimulated, they move by reflex action. I find my old results about the astonishing sensitiveness of the nervous system (!?) of Drosera to various stimulants fully confirmed and extended....
_C. D. 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, pepsine; 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....
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 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.
_The Kew Index of Plant-Names._
Some account of my father"s connection with the _Index of Plant-Names_, now (1892) being printed by the Clarendon Press, will be found in Mr. B.
Daydon Jackson"s paper in the _Journal of Botany_, 1887, p. 151. Mr.
Jackson quotes the following statement by Sir J. D. Hooker:--
"Shortly before his death, Mr. Charles Darwin informed Sir Joseph Hooker that it was his intention to devote a considerable sum of money annually for some years in aid or furtherance of some work or works of practical utility to biological science, and to make provisions in his will in the event of these not being completed during his lifetime.
"Amongst other objects connected with botanical science, Mr. Darwin regarded with especial interest the importance of a complete index to the names and authors of the genera and species of plants known to botanists, together with their native countries. Steudel"s _Nomenclator_ is the only existing work of this nature, and although now nearly half a century old, Mr. Darwin had found it of great aid in his own researches.
It has been indispensable to every botanical inst.i.tution, whether as a list of all known flowering plants, as an indication of their authors, or as a digest of botanical geography."