32 DROSERA ROTUNDIFOLIA. Cuar. II. 
into contact with the glands, and caused this rapid 
movement. Accordingly I added to some distilled 
water a pinch of a quite innocent substance, namely, 
precipitated carbonate of lime, which consists of an 
impalpable powder ; I shook the mixture, and thus got 
a fluid like thm milk. ‘wo 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 ad- 
hering to the external surface of the secretion. Some, 
however, had penetrated it, and were lying on the sur- 
faces of the glands; and no doubt it was these particles 
which caused the tentacles to bend. When a leaf is im- 
mersed 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 under- 
stand how the atoms of chalk, which rested on the 
surfaces of the glands, had penetrated the secretion. 
Anyone 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, 4; of an inch in length and weigh- 
ing 37's; of a grain, or of a human hair, =, of an 
inch in length and weighing only ,1,, of a grain 
(000822 milligramme), or particles of precipitated 
chalk, after resting for a short time on a gland, 
shculd induce some change in its cells, exciting them 
