28 DROSERA ROTUNDIFOLIA. [Cuar. IL. 
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 into contact 
with the glands, and caused this rapid movement. Accord- 
ingly I added to some distilled water a pinch of a quite inno- 
cent substance, namely, precipitated carbonate of lime, which 
consists of an impalpable powder; I shook the mixture, and 
thus got a fluid like thin milk. Two leaves were immersed 
in it, and in 6 m. almost every tentacle was much inflected. 
I placed one of these leaves under the microscope, and saw 
innumerable atoms of lime adhering to the external surface 
of the secretion. Some, however, had penetrated it, and 
were lying on the surfaces of the glands; and no doubt it 
was these particles which caused the tentacles to bend. 
When a leaf is immersed in water, the secretion instantly 
swells much; and I presume that it is ruptured here and 
there, so that little eddies of water rush in. If so, we can 
understand how the atoms of chalk, which rested on the 
surfaces of the glands, had penetrated the secretion. Any one 
who has rubbed precipitated chalk between his fingers will 
have perceived how excessively fine the powder is. No doubt 
there must be a limit, beyond which a particle would be too 
small to act on a gland; but what this limit is I know not. 
I have often seen fibres and dust, which had fallen from the 
air, on the glands of plants kept in my room, and these 
never induced any movement; but then such particles lay 
on the surface of the secretion and never reached the gland 
itself. 
Finally, it is an extraordinary fact that a little bit of soft 
thread, -), of an inch in length and weighing +!,, of a grain, 
or of a human hair, ,;44 of an inch in length and weighing 
only zg+zy Of a grain ('000822 milligram), or particles of 
precipitated chalk, after resting for a short time on a gland, 
should induce some change in its cells, exciting them to 
transmit a motor impulse throughout the whole length of the 
pedicel, consisting of about twenty cells, to near its base, 
causing this part to bend, and the tentacle to sweep through 
an angle of above 180°. That the contents of the cells of the 
