Umar. II THE PROCESS OF AGGREGATION. 59 
influence which induces aggregation should be trans- 
mitted at the proper rate from cell to cell. A plant, 
with its roots in water, was left for 45m. in a vessel 
containing 122 oz. of carbonic acid. <A leaf from this 
plant, and, for comparison, one from a fresh plant, were 
both immersed for 1 hr. in a rather strong solution 
of carbonate of ammonia. They were then compared, 
and certainly there was much less aggregation in the 
leaf which had been subjected to the carbonic acid 
than in the other. Another plant was exposed in 
the same vessel for 2 hrs. to. carbonic acid, and one of 
its leaves was then placed in a solution of one part of 
the carbonate to 437 of water; the glands were in- 
stantly blackened, showing that they had absorbed, 
and that their contents were aggregated; but in the 
cells close beneath the glands there was no aggre- 
gation even after an interval of 3hrs. After 4 hrs. 
15 m. a few minute spheres of protoplasm were formed 
in these cells, but even after 5 hrs. 30 m. the agegre- 
gation did not extend down the pedicels for a length 
equal to that of the glands. After numberless trials 
with fresh leaves immersed in a solution of this 
strength, I have never seen the aggregating action 
transmitted at nearly so slow a rate. Another plant 
was left for 2 hrs. in carbonic acid, but was then 
exposed for 20 m. to the open air, during which time 
the leaves, being of a red colour, would have absorbed 
some oxygen. One of them, as well as a fresh leaf 
for comparison, were now immersed in the same solu- 
tion as before. The former were looked at repeatedly, 
and after an interval of 65 m. a few spheres of 
protoplasm were first observed in the cells close be- 
neath the glands, but only in two or three of the 
longer tentacles. After 3 hrs. the aggregation had 
travelled down the pedicels of a few of the tentacles 
