190 ; DROSERA ROTUNDIFOLIA. (Cuar. X. 
that they cause reflection 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 various 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 
vf 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 glands, 
and only afew 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 @ 
larger number of tentacles, than the impulse from any single 
gland. 
* Transmission of the Motor Impulse—In every case the impulse 
from a gland has to travel for at least a short distance to the 
basal part of the tentacle, the upper part and the gland 
itself being merely carried by the inflection of the lower 
part. The impulse is thus always transmitted down nearly 
the whole length of the pedicel. When the central glands 
are stimulated, and the extreme marginal tentacles become 
