344 MISCELLANEOUS. [l88l. 



nitrate of potassium, another set with nitrate of sodium, and 

 another with nitrate of lime, giving all as much phosphate of 

 ammonia as they seemed to support, for I wish the plants to 

 grow as luxuriantly as possible. The plants watered with 

 nitrate of Na and of Ca would require, I suppose, some K ; but 

 perhaps they would get what is absolutely necessary from such 

 soil as I should be forced to employ, and from the rain-water 

 collected in tanks. I could use hard water from a deep well 

 in the chalk, but then all the plants would get lime. If the 

 plants to which I give Nitrate of Na and of Ca would not 

 grow I might give them a little alum. 



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 bears on the same 

 subject :] 



From C. Darwin to K. Semper* 



Down, July 19, 188 1. 



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 



* Professor of Zoology at Wiirz- title, ' The Natural Conditions ot 



burg. Existence as they affect Animal 



t Published in the ' International Life.' 

 Scientific Series/ in 1881, under the 



