26 DROSERA ROTUNDIFOLIA. [Cuar. IE. 
were exposed for a time naked to the air, but this caused no 
movement; yet these glands were in an efficient state, for, 
after 24 hrs. had elapsed, they were tried with bits of meat, 
and all became quickly inflected. It then occurred to me 
that particles floating on the secretion would cast shadows 
on the glands which might be sensitive to the interception 
of the light. Although this seemed highly improbable, as 
minute and thin splinters of colourless glass acted power- 
fully, nevertheless, after it was dark, I put on, by the aid of 
a single tallow candle, as quickly as possible, particles of 
cork and glass on the glands of a dozen tentacles, as well as 
some of meat on other glands, and covered them up so that 
not a ray of light could enter; but by the next morning, 
after 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 experi- 
ments, 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 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 
