Cuar. III] THE PROCESS OF AGGREGATION. 43 
of aggregation. One of these same leaves was then placed in a weak 
solution of the carbonate, and after 1 hr. 45 m. the tentacles for half 
their lengths showed an astonishing degree of aggregation. ‘I'wo other 
leaves were then placed in a much stronger solution of one part of the 
nitrate to 146 of water (8 grs. to 1 0z.); in one of these there was no 
marked change after 3 hrs.; but in the other there was a trace of 
aggregation after 52 m., and this was plainly marked after 1 hr. 22 m., 
but even after 2 hrs. 12 m. there was certainly not more aggregation 
than would have followed from an immersion of from 5 m. to 10 m. 
in an equally strong solution of the carbonate. 
Lastly, a leaf was placed in thirty minims of a solution of one part 
of phosphate of ammonia to 43,750 of water (1 gr. to 100 oz.), so that 
it received zg55 of a grain (-04079 mgr.); this soon caused the 
tentacles to be strongly inflected; and after 24 hrs. the contents of 
the cells were aggregated into oval and irregularly globular masses, 
with a conspicuous current of protoplasm flowing round the walls. 
But after so long an interval aggregation would have ensued, whatever 
had caused inflection. 
Only a few other salts, besides those of ammonia, were tried in 
relation to the process of aggregation. A leaf was placed in a solution 
of one part of chloride of sodium to 218 of water, and after 1 hr. the 
contents of the cells were aggregated into small, irregularly globular, 
brownish masses; these after 2 hrs. were almost disintegrated and 
pulpy. It was evident that the protoplasm had been injuriously 
affected ; and soon afterwards some of the cells appeared quite empty. 
These effects differ altogether from those produced by the several salts 
of ammonia, as well as by various organic fluids, and by inorganic 
particles placed on the glands. A solution of the same strength of 
carbonate of soda and carbonate of potash acted in nearly the same 
manner as the chloride; and here again, after 2 hrs. 80 m., the outer 
cells of some of the glands had emptied themselves of their brown 
pulpy contents. We shall see in the eighth chapter that solutions of 
several salts of soda of half the above strength cause inflection, but do 
not injure the leaves. Weak solutions of sulphate of quinine, of 
nicotine, camphor, poison of the cobra, &c., soon induce well-marked 
aggregation ; whereas certain other substances (for instance, a solution 
of curare) have no such tendency. 
Many acids, though much diluted, are poisonous; and though, as 
will be shown in the eighth chapter, they cause the tentacles to bend, 
they do not excite true aggregation. ‘hus leaves were placed in a 
solution of one part of benzoic acid to 487 of water; and in 15 m. the 
purple fluid within the cells had shrunk a little from the walls; yet, 
when carefully examined after 1 hr. 20 m., there was no true aggrega- 
tion; and after 24 hrs, the leaf was evidently dead. Other leaves in 
iodic acid, diluted to the same degree, showed after 2 hrs. 15 m. the 
same shrunken appearance of the purple fluid within the cells; and 
these, after G hrs, 15 m., were seen under a high power to be filled 
with excessively minute spheres of dull reddish protoplasm, which by 
