aggregate into small globular masses. I have seen a cloud of this kind
appear in 10 s. after a drop of a solution of carbonate of ammonia had
been given to a gland. With dark red leaves the first visible change
often is the conversion of the outer layer of the fluid within the
cells into bag-like masses. The aggregated masses, however they may
have been developed, incessantly change their forms and positions. They
are not filled with fluid, but are solid to their centres. Ultimately
the colourless granules in the protoplasm which flows round the walls
coalesce with the central spheres or masses; but there is still a
current of limpid fluid flowing within the cells. As soon as the
tentacles fully re-expand, the aggregated masses are redissolved, and
the cells become filled with homogeneous purple fluid, as they were at
first. The process of redissolution commences at the bases of the
tentacles, thence proceeding 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
* According to Hofmeister (as quoted by Sachs, Traite de Bot. 1874,
p. 958), very slight pressure on the cell-membrane arrests immediately
the movements of the protoplasm, and even determines its separation
from the walls. But the process of aggregation is a different
phenomenon, as it relates to the contents of the cells, and only
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 transmitted through this layer. [page 62]
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. If a
cell is ruptured, neither the exuded matter nor that which still
remains within the cell undergoes aggregation 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
54