object. Some force or influence must, therefore, be transmitted from
the central glands to the exterior tentacles, first to near their bases
causing this part to bend, and next to the glands causing them to
secrete more copiously. After a short time the glands, thus indirectly
excited, transmit or reflect some influence down their own pedicels,
inducing aggregation in cell beneath cell to their bases.
It seems at first sight a probable view that aggregation is due to the
glands being excited to secrete more copiously, so that sufficient
fluid is not left in their cells, and in the cells of the pedicels, to
hold the protoplasm in solution. In favour of this view is the fact
that aggregation follows the inflection of the tentacles, and during
the movement the glands generally, or, as I believe, always, secrete
more copiously than they did before. Again, during the re-expansion
[page 56] of the tentacles, the glands secrete less freely, or quite
cease to secrete, and the aggregated masses of protoplasm are then
redissolved. Moreover, when leaves are immersed in dense vegetable
solutions, or in glycerine, the fluid within the gland-cells passes
outwards, and there is aggregation; and when the leaves are afterwards
immersed in water, or in an innocuous fluid of less specific gravity
than water, the protoplasm is redissolved, and this, no doubt, is due
to endosmose.
Opposed to this view, that aggregation is caused by the outward passage
of fluid from the cells, are the following facts. There seems no close
relation between the degree of increased secretion and that of
aggregation. Thus a particle of sugar added to the secretion round a
gland causes a much greater increase of secretion, and much less
aggregation, than does a particle of carbonate of ammonia given in the
same manner. It does not appear probable that pure water would cause
much exosmose, and yet aggregation often follows from an immersion in
water of between 16 hrs. and 24 hrs., and always after from 24 hrs. to
48 hrs. Still less probable is it that water at a temperature of from
125 to 130 Fahr. (51 .6 to 54 .4 Cent.) should cause fluid to pass,
not only from the glands, but from all the cells of the tentacles down
to their bases, so quickly that aggregation is induced within 2 m. or 3
m. Another strong argument against this view is, that, after complete
aggregation, the spheres and oval masses of protoplasm float about in
an abundant supply of thin colourless fluid; so that at least the
latter stages of the process cannot be due to the want of fluid to hold
50