unap. IL INFLECTION INDIRECTLY CAUSED. 31 
elapsed. The remaining six tentacles never moved 
as long as they were observed; and the particles 
apparently never came into contact with the surfaces 
of the glands. 
From these experiments we learn that particles not 
containing soluble matter, when placed on glands, often 
cause the tentacles to begin bending in the course of 
from one to five minutes; and that in such cases the 
particles have been from the first in contact with the 
surfaces of the glands. When the tentacles do not 
begin moving for a much longer time, namely, from 
half an hour to three or four hours, the particles 
have been slowly brought into contact with the 
glands, either by the secretion being absorbed by the 
particles or by its gradual spreading over them, to- 
gether with its consequent quicker evaporation. 
When the tentacles do not move at all, the particles 
have never come into contact with the glands, or in 
some cases the tentacles may not have been in an 
active condition. In order to excite movement, it is 
indispensable that the particles should actually rest on 
the glands; for a touch once, twice, or even thrice 
repeated by any hard body is not sufficient to excite 
movement. 
Another experiment, showing that extremely mi- 
nute particles act on the glands when immersed in 
water, may here be given. A grain of sulphate of 
quinine was added to an ounce of water, which was 
not afterwards filtered; and on placing three leaves in 
ninety minims of this fluid, I was much surprised to find 
that all three leaves were greatly inflected in 15 m.; 
for I knew from previous trials that the solution does 
not act so quickly as this. It immediately occurred 
to me that the particles of the undissolved salt, which 
were so light as to float about, might have come 
