264 MR. C. DARWIN ON THE ACTION OF 
improbability in some of the protoplasm being withdrawn, to- 
gether with the imbedded granules, from the walls; for the 
whole of the protoplasm within the hairs of Tradescantia con- 
tracts, when subjected to great cold, into several spheres, and 
these, when warmed again, spread themselves out over the walls*. 
The process of aggregation commences in the gland which is 
stimulated, and slowly travels down the whole length of the 
tentacle, and even into the disk of the leaf, but very much more 
slowly than the impulse which causes the basal part of the ten- 
tacle to bend inwards. It isa more interesting fact that when 
the glands on the disk are stimulated, they transmit some in- 
fluence to the glands of the surrounding tentacles, which undergo 
throughout their whole length the process of aggregation, 
although they themselves have not been directly stimulated; 
and this process may be compared with a reflex action in the 
nervous system of an animal. After a few days the solid aggre- 
gated masses are redissolved. The process of redissolution 
commences in the cells at the bases of the tentacles and travels 
slowly upwards ; therefore in a reversed direction to that of aggre- 
gation. Considering that the aggregated masses are solid enough 
to be broken into fragments, their prompt redissolution is a 
surprising fact; and we are led to suspect that some ferment 
must be generated in the disk of the leaf, and be transmitted 
up the tentacles. The double process of aggregation and of 
redissolution takes place every time that a leaf of Drosera 
catches an insect. 
Aggregation is a vital process—that is, it cannot occur in 
cells after their death. This was shown by waving leaves f 
for a few minutes in water at a temperature of 65^5 C. (150? RÄ 
or even at a somewhat lower temperature, and then immers- 
ing them in a rather strong solution of carbonate of ammonia, 
which does not cause in this case any aggregation, although 
the most powerful of all known agents. It a tentacle is 
slightly erushed, so that many of the cells are ruptured, though 
they still retain much of their purple fluid contents, no aggre- 
gation occurs in them when they are similarly immersed, not- 
* Van Tieghem, * Traité de Botanique, 1882, p. 596. See also p. 528, on 
masses of protoplasm floating freely within the cavities of cells. Sachs (‘ Phy- 
siologie Végétale, p. 74) and Kühne (‘Das Protoplasma, p. 103) have likewise 
seen small freely-floating masses of protoplasm in the hairs of Tradescantia and 
Cucurbita which undergo amceboid changes of form. 
T 'Insectivorous Plants, p. 58, 
