516 MISCELLANEOUS BOTANICAL LETTERS, [1881, 



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 pro- 

 cure ? 



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 * bears on the same 

 subject :] 



From C. 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.f 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 pro- 

 duced by cultivating certain plants under unnatural condi- 

 tions, as the presence of salt, lime, zinc, &c., &c., 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 



* Professor of Zoology at Wiirzburg. 



t Published in the ' International Scientific Series,' in 1881, under the 

 title, ' The Natural Conditions of Existence as they affect Animal Life ' 



