an interval of 13 hrs., all the particles were carried to the centres
of the leaves.
These negative results led me to try many more experiments, by placing
particles on the surface of the drops of secretion, observing, as
carefully as I could, whether they penetrated it and touched the
surface of the glands. The secretion, from its weight, generally forms
a thicker layer on the under than on the upper sides of the glands,
whatever may be the position of the tentacles. Minute bits of dry cork,
thread, blotting paper, and coal cinders were tried, such as those
previously employed; and I now observed that they absorbed much more of
the secretion, in the course of a few minutes, than I should have
thought possible; and as they had been laid on the upper surface of the
secretion, where it is thinnest, they were often drawn down, after a
time, into contact with at least some one point of the gland. With
respect to the minute splinters of glass and particles of hair, I
observed that the secretion slowly spread itself a little over their
surfaces, by which means they were likewise drawn downwards or
sideways, and thus one end, or some minute [page 30] prominence, often
came to touch, sooner or later, the gland.
In the foregoing and following cases, it is probable that the
vibrations, to which the furniture in every room is continually liable,
aids in bringing the particles into contact with the glands. But as it
was sometimes difficult, owing to the refraction of the secretion, to
feel sure whether the particles were in contact, I tried the following
experiment. Unusually minute particles of glass, hair, and cork, were
gently placed on the drops round several glands, and very few of the
tentacles moved. Those which were not affected were left for about half
an hour, and the particles were then disturbed or tilted up several
times with a fine needle under the microscope, the glands not being
touched. And now in the course of a few minutes almost all the hitherto
motionless tentacles began to move; and this, no doubt, was caused by
one end or some prominence of the particles having come into contact
with the surface of the glands. But as the particles were unusually
minute, the movement was small.
Lastly, some dark blue glass pounded into fine splinters was used, in
order that the points of the particles might be better distinguished
when immersed in the secretion; and thirteen such particles were placed
28