. Cuar. VIL] NITRATE OF AMMONIA. ‘121 
half-minims (-0296 ¢.c.) on the discs of fifty-two leaves, but will give 
only a few cases. A solution of one part to 109 of water was too strong, 
causing little inflection, and after 24 hrs. killing, or nearly killing, 
four out of six leaves which were thus tried; each of which received 
the 545 of a grain (or ‘27 mg.). A solution of one part to 218 of 
water acted most energetically, causing not only the tentacles of all the 
lcaves, but the blades of some to be strongly inflected. J’ourteen leaves 
were tried with drops of a solution of one part to 875 of water, so that the 
dis2 of each received the ,g4, of a grain (*0337 mg.). Of these leaves, 
seven were very strongly acted on, the edges beiny generally inflected ; 
two were moderately acted on; and five notat all. I subsequently tried 
three of these latter five leaves with urine, saliva, and mucus, but they 
were only slightly affected ; and this proves that they were not in an 
active condition. I mention this fact to show how necessary it is to 
experiment on several leaves. Two of the leaves, which were well 
intlected, re-expanded after 51 hrs. 
In the following experiment I happened to select very sensitive 
leaves. Half-minims of a solution of one part to 1094 of water (de. 
1 gr. to 23 oz.) were placed on the discs of nine leaves, so that each 
received the 755 of a grain (:027 mg.). ‘I'hree of them had their 
tentacles strongly inflected and their blades curled inwards; five were 
slightly and somewhat doubtfully affected, having from three to eight 
of their exterior tentacles intlected; one leaf was not at all affected, 
yet was afterwards acted on by saliva. In six of these cases, a trace of 
action was perceptible in 7 hrs., but the full effect was not produced until 
from 24 hrs, tu 80 hrs. had elapsed. ‘Two of the leaves, which were only 
slightly inflected, re-expanded after an additional interval of 19 hrs. 
Half-minims of a rather weaker solution, viz. of one part to 1312 
of water (1 gr. to 3 oz.) were tried on fourteen leaves; so that each 
received g;izg of a grain ("0224 mg.), instead of, as in the last experi- 
ment, gz5q of a grain. ‘Ihe blade of one was plainly inflected, as were 
six of the exterior tentacles; the blade of a second was slightly, and 
two of the exterior tentacles well inflected, all the other tentacles 
being curled in at right angles to the disc; three other leaves had from 
live to eight tentacles inflected; five others only two or three, and 
cecasionally, though very rarely, drops of pure water cause this much 
action; the four remaining leaves were in no way affected, yet three of 
them, when subsequently tried with urine, became greatly inflected. 
In most of these cases a slight effect was perceptible in from 6 hrs. to 
7 hrs., but the full effect was not produced until from 24 hrs. to 30 
lirs. had elapsed. It is obvious that we have reached very nearly the 
minimum amount, which, distributed between the glands of the disc, 
acts on the exterior tentacles; these having themselves not received 
any of the solution. ‘ 
In the next place, the viscid secretion round three of the exterior 
g'ands was touched with the same little drop (s'5 of a minim) of a 
solution of one part to 437 of water; and after an interval of 2 hrs. 
60 m. all three tentacles were well inflected. Each of these glands 
