52 DROSERA ROTUNDIFOLIA. (Cuapr. IIL 
redissolved, and the cells become filled with homogeneous 
purple fluid, as they were at first. The process of redissolu- 
tion commences at the bases of the tentacles, thence pro- 
ceeding upwards to the glands; and, therefore, in a reversed 
direction to that of aggregation. 
Aggregation is excited by the most diversified causes,— 
by the glands being several times touched,—by the pressure 
of particles of any kind, and as these are supported by the 
dense secretion, they can hardly press on the glands with the 
weight of a millionth of a grain,*—by the tentacles being 
cut off close beneath the glands,—by the glands absorbing 
various fluids or matter dissolved out of certain bodies,—by 
exosmose,—and by a certain degree of heat. On the other 
hand, a temperature of about 150° Fahr. (65°°5 Cent.) does 
not excite aggregation; nor does the sudden crushing of a 
gland. Ifacell is ruptured, neither the exuded matter nor 
that which still remains within the cell undergoes aggrega- 
tion when carbonate of ammonia is added. A very strong 
solution of this salt and rather large bits of raw meat prevent 
the aggregated masses being well developed. From these 
facts we may conclude that the protoplasmic fluid within a 
cell does not become aggregated unless it be in a living state, 
and only imperfectly if the cell has been injured. We have 
also seen that the fluid must be in an oxygenated state, 
in order that the process of aggregation should travel from 
cell to cell at the proper rate. 
Various nitrogenous organic fluids and salts of ammonia 
induce aggregation, but in different degrees and at very 
different rates. Carbonate of ammonia is the most powerful 
of all known substances; the absorption of y5-2 of a 
grain (000482 mg.) by a gland suffices to cause all the cells 
of the same tentacle to become aggregated. The first effect 
of the carbonate and of certain other salts of ammonia, as well 
as of some other fluids, is the darkening or blackening of the 
glands. This follows even from long immersion in cold 
* According to Hofmeister (as 
quoted by Sachs, ‘Traité de Bot.,’ oe a a aa 
contents of the cells, and only 
1874, p. 958), very slight pressure 
on the cell-membrane arrests imme- 
diately the movements of the pro- 
toplasm, and even determines its 
separation from the walls. But the 
process of aggregation is a different 
secondarily to the layer of protoplasm 
which flows along the walls; though 
no doubt the effects of pressure or of 
a touch on the outside must be trans- 
mitted through this layer. 
