aiaa patie 
ee ye 
— 
Cumar. VIL] EFFECTS OF WATER. 113 
until some time had elapsed, instead of within half an hour, or even 
within a few minutes, as usually occurred. All the glands on tke 
same leaf are of nearly the same size, as may best be seen by cutting 
off a narrow transverse strip, and laying it on its side; hence their 
absorbing surfaces are nearly equal. The iong-headed glands on the 
extreme margin must be excepted, as they are much longer than the 
others; but only the upper surface is capable of absorption. Besides 
the glands, both surfaces of the leaves and the pedicels of the tentacles 
bear numerous minute papillæ, which absorb carbonate of ammonia, 
an infusion of raw meat, metallic salts, and probably many other 
substances, but the absorption of matter by these papillæ never induces 
inflection. We must remember that the movement of each separate 
tentacle depends on its gland being excited, except when a motor 
impulse is transmitted from the glands of the disc, and then the 
movement, as just stated, does not take place until some little time 
has elapsed. I have made these remarks because they show us that 
when a leaf is immersed in a solution, and the tentacles are inflected, 
we can judge with some accuracy how much of the salt each gland 
has absorbed. For instance, if a leaf bearing 212 glands, be immersed 
in a measured quantity of a solution, containing , of a grain of a salt, 
and all the exterior tentacles, except twelve, are inflected, we may 
feel sure that each of the 200 glands can on an average have absorbed 
at most sg, of a grain of the salt. I say at most, for the papilla 
will have absorbed some small amount, and so will perhaps the glands 
of the twelve excluded tentacles which did not become intlected. ‘The 
application of this principle leads to remarkable conclusions with 
respect to the minuteness of the doses causing inflection. 
On the Action of Distilled Water in causing Inflection. 
Although in all the more important experiments the difference 
between the leaves simultaneously immersed in water and in the 
several solutions will be described, nevertheless it may be well here 
to give a summary of the effects of water. ‘lhe fact, moreover, of 
pure water acting on the glands deserves in itself some notice. Leaves 
to the number of 141 were immersed in water at the same time with 
those in the solutions, and their state recorded at short intervals of 
time. Thirty-two other leaves were separately observed in water, 
making altogether 173 experiments. Many scores of leaves were also 
immersed in water at other times, but no exact record of the effects 
produced was kept; yet these cursory observations support the con- 
clusions arrived at in thischapter. A few of the long-headed tentacles, 
namely from one to about six, were commonly inflected within half 
an hour after immersion; as were occasionally a few, and rarely a 
considerable number of the exterior round-headed tentacles. After an 
immersion of from 5 to 8 hrs. the short tentacles surrounding the 
outer parts of the disc generally become inflected, so that their glands 
form a small dark ring on the disc; the exterior tentacles not par- 
I 
