al suffering in
consequence of the potato disease than has any other from the same
cause. Although this disease has never, in this country, prevailed to
the same ruinous extent that it has in some others, yet we are yearly
reminded of its existence, and in some seasons and localities its
destructive effects are seriously apparent.

The final or culminating cause of the disease known as the "potato-rot"
is _Botrytis (peronospora) infestans_. This may be induced by many and
various predisposing causes, such as feebleness of constitution of the
variety planted, rendering them an easy prey to the disease; by planting
on low, moist land, or on land highly enriched by nitrogenous manures,
causing a morbid growth which invites the disease; also by insects or
their larvae puncturing or eating off the leaves or vines. But by far the
most wide-spread and most common cause of the disease is sudden changes
of atmospheric temperature, particularly when accompanied by rain.
Drought, though quite protracted and severe, unless accompanied by
strong drying winds, and followed by sudden and great reduction of
temperature, seldom affects the potato seriously. It is not uncommon in
the Northern States, during the months of August and September, for
strong westerly winds to prevail for many days in succession. These
winds, coming from the great American desert, are almost wholly devoid
of moisture, and their aridity is often such that vegetation withers
before them as at the touch of fire. Evaporation is increased in a
prodigiously rapid ratio with the velocity of wind. The effects of the
excessive exhalation from the leaves of plants exposed to the sweep of
such drying winds are at once seriously apparent.

When these winds finally cease, the atmosphere has a low relative
humidity, not enough moisture remains in the air to prevent radiation;
the heat absorbed by the earth through the day is, during the bright,
cloudless night, rapidly radiated and lost in space, and a reduction in
temperature of twenty to thirty degrees is the consequence.

In the first place, the potato-vines suffer by excessive exhalation; in
the second, by sudden reduction of temperature, and, though not frozen,
their functions are much deranged, and their vitality greatly enfeebled.
To use a common expression, the plant "has caught a violent cold that
has settled on the lungs."

The leaves (which are the lungs of plants) now fail to perform their
functions properly