I am well aware how very ignorant I am, and how crude my notions are; and if you could suggest any other solutions by which plants would be likely to be affected it would be a very great kindness. I suppose that there are no organic fluids which plants would absorb, and which I could procure?
I must trust to your kindness to excuse me for troubling you at such length, and,
I remain, dear Sir, yours sincerely, CHARLES DARWIN.
[The next letter to Professor Semper (Professor of Zoology at Wurzburg.) bears on the same subject:]
FROM
CHARLES DARWIN TO K. SEMPER. Down, July 19, 1881.
My dear Professor Semper,
I have been much pleased to receive your letter, but I did not expect you to answer my former one... I cannot remember what I wrote to you, but I am sure that it must have expressed the interest which I felt in reading your book. (Published in the 'International Scientific Series,' in 1881, under the title, 'The Natural Conditions of Existence as they affect Animal Life.') I thought that you attributed too much weight to the DIRECT action of the environment; but whether I said so I know not, for without being asked I should have thought it presumptuous to have criticised your book, nor should I now say so had I not during the last few days been struck with Professor Hoffmann's review of his own work in the 'Botanische Zeitung,' on the variability of plants; and it is really surprising how little effect he produced by cultivating certain plants under unnatural conditions, as the presence of salt, lime, zinc, etc., etc., during SEVERAL generations. Plants, moreover, were selected which were the most likely to vary under such conditions, judging from the existence of closely-allied forms adapted for these conditions. No doubt I originally attributed too little weight to the direct action of conditions, but Hoffmann's paper has staggered me. Perhaps hundreds of generations of exposure are necessary. It is a most perplexing subject. I wish I was not so old, and had more strength, for I see lines of research to follow. Hoffmann even doubts whether plants vary more under cultivation than in their native home and under their natural conditions. If so, the astonishing variations of almost all cultivated plants must be due to selection and breeding from the varying individuals. This idea crossed my mind many years ago, but I was afraid to publish it, as I thought that people would say, "how he does exaggerate the importance of selection."
I still MUST believe that changed conditions give the impulse to variability, but that they act IN MOST CASES in a very indirect manner. But, as I said, it is a most perplexing problem. Pray forgive me for writing at such length; I had no intention of doing so when I sat down to write.
I am extremely sorry to hear, for your own sake and for that of Science, that you are so hard worked, and that so much of your time is consumed in official labour.
Pray believe me, dear Professor Semper, Yours sincerely, CHARLES DARWIN.