the leaves of plants with their roots still in damp earth, no inflection ensues, for the roots, no doubt, pump up water as quickly as it is lost by exosmose.  But if cut-off leaves are immersed in syrup, or in any dense fluid, the tentacles are greatly, though irregularly, inflected, some of them assuming the shape of corkscrews; and the leaves soon become flaccid.  If they are now immersed in a fluid of low specific gravity, the tentacles re-expand.  From these [page 233] facts we may conclude that drops of syrup placed on the backs of leaves do not act by exciting a motor impulse which is transmitted to the tentacles; but that they cause reflexion by inducing exosmose.  Dr. Nitschke used the secretion for sticking insects to the backs of the leaves; and I suppose that he used a large quantity, which from being dense probably caused exosmose.  Perhaps he experimented on cut-off leaves, or on plants with their roots not supplied with enough water.

As far, therefore, as our present knowledge serves, we may conclude that the glands, together with the immediately underlying cells of the tentacles, are the exclusive seats of that irritability or sensitiveness with which the leaves are endowed.  The degree to which a gland is excited can be measured only by the number of the surrounding tentacles which are inflected, and by the amount and rate of their movement.  Equally vigorous leaves, exposed to the same temperature (and this is an important condition), are excited in different degrees under the following circumstances.  A minute quantity of a weak solution produces no effect; add more, or give a rather stronger solution, and the tentacles bend.  Touch a gland once or twice, and no movement follows; touch it three or four times, and the tentacle becomes inflected.  But the nature of the substance which is given is a very important element:  if equal-sized particles of glass (which acts only mechanically), of gelatine, and raw meat, are placed on the discs of several leaves, the meat causes far more rapid, energetic, and widely extended movement than the two former substances.  The number of glands which are excited also makes a great difference in the result:  place a bit of meat on one or two of the discal [page 234] glands, and only a few of the immediately surrounding short tentacles are inflected; place it on several glands, and many more are acted on; place it on thirty or forty, and all the tentacles, including the extreme marginal ones, become closely inflected.  We thus see that the impulses proceeding from a number of glands strengthen one another, spread farther, and act on a larger number of tentacles, than the impulse from any single gland.