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SEASIDE PLANTS.
plasmic contents of the unbroken cells contract and withdraw
from the cell-walls, the space between the walls and the con-
tracted cell-contents being occupied by the solution of salt. In
fact the living protoplasm is unable to absorb the salt and has
actually to give up some of the water with which it is saturated
to the hygroscopic salt-solution around it. If, on the other hand,
we kill the protoplasm, by boiling or by the application of acid,
before applying the salt solution we find that the latter diffuses
readily into the dead cell-contents and there is no such contrac-
tion as in the first case.
This indicates that plants whose roots are supplied with
salt-water are able to assimilate for purpose of nutrition but a
very little of the water which reaches them: they are to a great
extent subjected to a water famine; and they have developed—
in many different Natural Orders—water-saving structures.
Chemical analysis shows us that the plants have no choice in
this matter. As the sea water is rich in salts of soda, so the ash
of these sea-side plants is rich in soda ; but it can readily be
demonstrated that most, if not all, of this soda is physiologically
useless to the plant, which cannot, however, refuse to absorb it.
Not only do experiments in growing plants in prepared solutions
demonstrate that they can maintain their full health and vitality
while dispensing with soda ; but when a sea-side plant, such as
Asparagus, which occurs on another part of our Essex coast, is
transferred into ordinary inland garden mould, which is rich in
potash but poor in soda, the soda in the plant-ash rapidly
becomes replaced by potash. It is, however, important to bear
in mind that the converse of this experiment, the replacement of
potash by soda, cannot be performed, some potash being appar-
ently essential to the life of every flowering plant.
Succulence is not, however, the only adaptation to the
economising water of which we have seen examples to-day. In
several species of grass, such as the Marram (Psamma arenaria)
and the Lyme Grass (Elymus arenarius), which grow near the sea,
we find the leaves are rolled up and their surface, not only
"glaucous," or covered with grey bloom, but marked by deep
longitudinal grooves. To these grooves the few stomata are
confined, and, in some cases, hairs lining the grooves would
seem to be a special contrivance to re-absorb the moisture
directly it has been transpired by the protected stomata.