ence. Ozone, supposed to be a peculiar form of
oxygen, is exhaled from every part of the green surface of plants in
health, and effectually repels the attacks of mildew; but it is found
that when the atmosphere is very dry, or, on the other hand, very humid,
plants cease to evolve ozone, and are therefore unprotected. Winds from
the ocean are strongly ozonic, and it is ascertained that plants growing
on soil to which salt has been applied evolve more ozone than others.
Hence the benefit derived from the use of salt on potato lands.

The "Black knot," another species of fungus that attacks the branches of
the plum and Morello cherry, operates very similarly to the potato
mildew. The roots of the parasite penetrate and split up the cellular
tissue of the branch on which it fastens, and if the limb be not
promptly amputated, the descending sap carries the deleterious principle
through the whole system, and the following year the disease appears in
a greatly aggravated form in every part of the whole tree. The remedy in
this case is prompt amputation of the part diseased on its first
appearance, and a judicious application of salt to the soil.

Common salt, to a certain extent, is as beneficial to some plants as to
animals; and every intelligent farmer knows that if salt be withheld
from the bovine _genus_ for any considerable length of time, the general
health droops and parasites are sure to abound. The object of nature in
bringing into existence the large family of mildews, each member of
which is a perfect plant in its way, and as capable of performing its
functions as the oak of the forest, was undoubtedly to prevent
propagation from sickly stock, and by the decomposition of feeble plants
to make room and enrich the soil for the better development of
healthier plants. But it by no means follows that, because a plant is
attacked by mildew, it must necessarily be left to die, any more than it
follows that, because an animal is infested with vermin, it should be
let alone to be eaten up by them.

REMEDY FOR THE POTATO-ROT.

In treating for the potato-rot, "an ounce of prevention is worth a pound
of cure;" for when leaves or vines are once dead, they ever remain so.
All that can be done for potatoes infested is to stop the mildew from
spreading, by destroying it where it is, and by strengthening "those
things which remain." The writer was led to the adoption of the remedy
proposed by experiments made upon fruits.

E