Cuap. VIL 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 
so 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 seere- 
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 J, of a minim. Some water in a 
small vessel was weighed (and this is a more accurate method), 
and 800 drops removed as beforé; and on again weighing the 
water, a drop was found to equal on an average only the 2; 
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 = of a minim. I repeated the operation in 
exactly the same manner, and now the drops averaged 33 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 j, 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 
