or of a vital process. In the first case the
action of the hydathode should continue even after the treatment with
the sublimate solution, while in the latter case it should not. As the
secretion ceased the obvious conclusion to be deduced from this
experiment is that the hydathodes do not act as purely mechanical
filtration-apparatuses, as one might have thought, but that there is
here evidence of an active vital process in the plant; the unusual term
"poisoning" is therefore really justified under present circumstances.

Let me dwell for a moment on this result, for, although it may be
somewhat foreign to our present purpose and to the further observations
of Haberlandt, it is very significant in itself. The water moves in the
plant in closed cells, as the cells of the aqueous gland are entirely
closed, but the organic membrane, as every one knows, has the peculiar
physical property of allowing water to pass through, the pressure, of
course, being applied on the side of least resistance; when therefore
the water is forced into the cells by root-pressure, it is easily
intelligible that according to purely physical laws it should come to
the surface of the leaf on the side of the least resistance, that is,
by way of the water-crevices. Even the defenders of "vital force" would
not find any reason in this for not considering the phenomenon of
distillation in this case a purely physical phenomenon. And still
according to Haberlandt's experiments it is not. The sublimate could at
most only impede the process of filtration, but should under no
circumstances have destroyed it. But it does destroy it, and the
hydathode dies. The conclusion certainly follows from this that this
process is connected with some vital function. Even if the hydathode is
treated with sublimate solution, all the conditions for mechanical
filtration still remain: the earth has moisture which can be taken up
by the roots so that root-pressure still exists. The water is in all
cases conveyed to the hydathodes through the vascular fibres, the cell
walls of the hydathodes are still adapted for filtration, and yet they
do not filter. Hence some other factor must join itself to the
physico-mechanical process of filtration and affect or destroy it, and
this factor can be found only in the protoplasm, the vital element of
the cells; for we know that the sublimate acts with pernicious effect
on it and in such a manner that it destroys its entire power of
react