Cuar. I. ACTION OF THE PARTS. 18 
well as the blade remain inflected over an object placed 
on the disc, depends on various circumstances; namely 
on the vigour and age of the leaf, and, according to 
Dr. Nitschke, on the temperature, for during cold 
weather when the leaves are inactive, they re-expand 
at an earlier period than when the weather is warm. 
But the nature of the object is by far the most 
important circumstance; I have repeatedly found that 
the tentacles remain clasped for a much longer average 
time over objects which yield soluble nitrogenous 
matter than over those, whether organic or inorganic, 
which yield no such matter. After a period varying 
from one to seven days, the tentacles and blade re- 
expand, and are then ready to act again. I have seen 
the same leaf inflected three successive times over 
insects placed on the disc; and it would probably 
have acted a greater number of times. 
The secretion from the glands is extremely viscid, 
so that it can be drawn out into long threads. It 
appears colourless, but stains little balls of paper pale 
pink. An object of any kind placed on a gland always 
causes it, as I believe, to secrete more freely; but 
the mere presence of the object renders this difficult 
to ascertain. In some cases, however, the effect was 
strongly marked, as when particles of sugar were 
added; but the result in this case is probably due 
merely to exosmose. Particles of carbonate and phos- 
phate of ammonia and of some other salts, for instance 
sulphate of zinc, likewise increase the secretion. Im- 
mersion in a solution of one part of chloride of gold, 
or of some other salts, to 487 of water, excites the 
glands to largely increased secretion; on the other 
hand, tartrate of antimony produces no such effect. 
-mmersion in many acids (of the strength of one part 
to 4387 of water) likewise causes a wonderful amount of 
