CIIAP. VII. SALTS OF AMMONIA. 137 



discs of the leaves, and the inflection of the exterior rows of 

 tentacles observed at successive intervals of time. It was first 

 ascertained, from between thirty and forty trials, that distilled 

 water dropped in this manner produces no effect, except that 

 sometimes, though rarely, two or three tentacles become in- 

 flected. In fact all the many trials with solutions which were 

 *o weak as to produce no effect lead to the same result that 

 water is inefficient. 



Secondly. The head of a small pin, fixed into a handle, was 

 dipped into the solution under trial. The small drop which 

 adhered to it, and which was much too small to fall off, was 

 cautiously placed, by the aid of a lens, in contact with the secre- 

 tion surrounding the glands of one, two, three, or four of the 

 exterior tentacles of the same leaf. Great care was taken that 

 the glands themselves should not be touched. I had supposed 

 that the drops were of nearly the same size ; but on trial this 

 proved a great mistake. I first measured some water, and re- 

 moved 300 drops, touching the pin's head each time on blotting- 

 paper ; and on again measuring the water, a drop was found to 

 equal on an average about the ^ of a minim. Some water in a 

 small vessel was weighed (and this is a more accurate method), 

 and 300 drops removed as before ; and on again weighing the 

 water, a drop was found to equal on an average only the -^ 

 of a minim. I repeated the operation, but endeavoured this 

 time, by taking the pin's head out of the water obliquely and 

 rather quickly, to remove as large drops as possible ; and 

 the result showed that I had succeeded, for each drop on an 

 average equalled YJTJ of a minim. I repeated the operation in 

 exactly the same manner, and now the drops averaged 7^ of a 

 minim. Bearing in mind that on these two latter occasions 

 special pains were taken to remove as large drops as possible, 

 we may safely conclude that the drops used in my experiments 

 were at least equal to the -^ of a minim, or *0029 ml. One of 

 these drops could be applied to three or even four glands, and 

 if the tentacles became inflected, some of the solution must 

 have been absorbed by all; for drops of pure water, applied 

 in the same manner, never produced any effect. I was able to 

 hold the drop in steady contact with the secretion only for ten 

 to fifteen seconds ; and this was not time enough for the diffu- 

 sion of all the salt in solution, as was evident, from three or 

 four tentacles treated successively with the same drop, often 

 becoming inflected. All the matter in solution was even then 

 probably not exhausted. 



Thirdly. Leaves were cut off and immersed in a measured 



