i86o.] CLIMBING AND INSECTIVOROUS PLANTS. 491 



lous. You will laugh ; but it is, at present, my full belief 

 (after endless experiments) that they detect (and move in 

 consequence of) the ^sVo P^^^ c)f 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 ! I began this work on Drosera in re- 

 lation Xo gradation as throwing light on Dionsea." 



Later in the autumn he was again obliged to leave home 

 for Eastbourne, where he continued his work on Drosera. 

 The work was so new to him that he found himself in diffi- 

 culties in the preparation of solutions, and became puzzled 

 over fluid and solid ounces, &c. &c. To a friend, the late 

 Mr. E. Cresy, who came to his help in the matter of weights 

 and measures, he wrote giving an account of the experiments. 

 The extract (November 2, i860) which follows illustrates 

 the almost superstitious precautions he often applied to his 

 researches : — 



" Generally I have scrutinised every gland and hair on the 

 leaf before experimenting ; but it occurred to me that I might 

 in some way affect the leaf ; though this is almost impossible, 

 as I scrutinised with equal care those that I put into distilled 

 water (the same water being used for dissolving the carbonate 

 of ammonia). I then cut off four leaves (not touching them 

 with my fingers), and put them in plain water, and four other 

 leaves into the weak solution, and after leaving them for an 

 hour and a half, I examined every hair on all eight leaves ; 

 no change on the four in water ; every gland and hair affected 

 in those in ammonia. 



*' I had measured the quantity of weak solution, and I 

 counted the glands which had absorbed the ammonia, and 

 were plainly affected ; the result convinced me that each 

 gland could not have absorbed more than ^i\(i^ or ^g^^q of 

 a grain. I have tried numbers of other experiments all 

 pointing to the same result. Some experiments lead me to 

 believe that very sensitive leaves are acted on by much 

 smaller doses. Reflect how little ammonia a plant can get 

 growing on poor soil — yet it is nourished. The really sur- 



