Plants of duck-weed (Lemna) were left for between 30 m. and 45 m. in a
solution of one part of this same salt to 146 of water, and three of
their roots were then examined. In two of them, all the cells which had
previously contained only limpid fluid now included little green
spheres. After from 1 1/2 hr. to 2 hrs. similar spheres appeared in the
cells on the borders of the leaves; but whether the ammonia had
travelled up the roots or had been directly absorbed by the leaves, I
cannot say. As one species, Lemna arrhiza, produces no roots, the
latter alternative is perhaps the most probable. After about 2 1/2 hrs.
some of the little green spheres in the roots were broken up into small
granules which exhibited Brownian movements. Some duck-weed was also
left for 1 hr. 30 m. in a solution of one part of [page 65] carbonate
of potash to 218 of water, and no decided change could be perceived in
the cells of the roots; but when these same roots were placed for 25 m.
in a solution of carbonate of ammonia of the same strength, little
green spheres were formed.
A green marine alga was left for some time in this same solution, but
was very doubtfully affected. On the other hand, a red marine alga,
with finely pinnated fronds, was strongly affected. The contents of the
cells aggregated themselves into broken rings, still of a red colour,
which very slowly and slightly changed their shapes, and the central
spaces within these rings became cloudy with red granular matter. The
facts here given (whether they are new, I know not) indicate that
interesting results would perhaps be gained by observing the action of
various saline solutions and other fluids on the roots of plants. [page
66]
CHAPTER IV.
THE EFFECTS OF HEAT ON THE LEAVES.
Nature of the experiments Effects of boiling water Warm water causes
rapid inflection Water at a higher temperature does not cause immediate
inflection, but does not kill the leaves, as shown by their subsequent
re-expansion and by the aggregation of the protoplasm A still higher
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