Cuap. VIL CARBONATE OF AMMONIA. 141 
this again is so rare a circumstance with leaves in water that 
I have seen only three instances of any such increase after the 
first 8 to 12 hrs.; and in these three instances the two outer 
rows of tentacles were not at all affected. Hence there is some- 
times a much greater difference between the leaves in water and 
in the weak solutions, after from 8 hrs. to 24 hrs., than there 
was within the first 3 hrs.; though as a general rule it is best 
to trustto the difference observed within the shorter time. 
With respect to the period of the re-expansion of the leaves, 
when left immersed either in water or in the weak solutions, 
nothing could be more variable. In both cases the exterior 
tentacles not rarely begin to re-expand, after an interval of 
only from 6 to 8 hrs.; that is just about the time when the 
short tentacles round the borders of the disc become inflected. 
On the other hand, the tentacles sometimes remain inflected 
for a whole day, or even two days; but as a general rule they 
remain inflected for a longer period in very weak solutions than 
in water. In solutions which are not extremely weak, they 
never re-expand within nearly so short a period as six or 
eight hours. From these statements it might be thought 
difficult to distinguish between the effects of water and the 
weaker solutions; but in truth there is not the slightest diffi- 
culty until excessively weak solutions are tried; and then the 
distinction, as might be expected, becomes very doubtful, and 
at last disappears. But as in all, except the simplest, cases 
the state of the leaves simultaneously immersed for an equal 
length of time in water and in the solutions will be described, 
the reader can judge for himself. 
CARBONATE OF AMMONIA. 
This salt, when absorbed by the roots, does not cause 
the tentacles to be inflected. A plant was so placed 
in a solution of one part of the carbonate to 146 of 
water that the young uninjured roots could be ob- 
served. The terminal cells, which were of a pink 
colour, instantly became colourless, and their limpid 
contents cloudy, like a mezzo-tinto engraving, so that 
some degree of aggregation was almost instantly 
caused; but no further change ensued, and the ab- 
sorbent hairs were not visibly affected. The tentacles 
