finally kill it. The remedy for this is to spray the leaves frequently
so as to keep the air about them moist and so check transpiration.
Keeping a vessel of water near them helps also as this tends to keep
the air moist. Dust sometimes chokes the leaves. Washing or spraying
remedies this.

Sometimes house plants, and out-door plants as well, become covered
with a small, green insect called the plant louse or aphis. This
insect has a sharp beak like a mosquito and it sucks the juices from
the leaf and causes it to curl up, interfering with its work and
finally killing it. Frequent spraying with water will tend to keep
these away. A surer remedy against them is to spray the plants with
weak tobacco water made by soaking tobacco or snuff in water, or to
fumigate them with tobacco smoke. Sometimes the under side of the
leaf becomes infested with a very small mite called red spider
because it spins a web. These mites injure the leaf by sucking sap
from it. They can be kept in check by frequent spraying for they do
not like water. If, then, we are careful to frequently spray the
leaves of our house plants we will have very little trouble from
aphis, red spider or over transpiration. The aphis, or plant louse, is
often very numerous on out-door plants, for instance, the rose,
chrysanthemum, cabbage, and fruit trees. They vary in color from green
to dark brown or black. They are treated in the same way as those on
the house plants. Some familiar out-door insects which interfere with
leaf work are the common potato bug, the green cabbage worm, the rose
slug, the elm tree leaf beetle, the canker worm, the tomato worm.
These insects and many others eat the leaves (Fig. 67). They chew and
swallow their food and are called chewing insects. All insects which
chew the leaves of plants can be destroyed by putting poison on their
food. The common poisons used for this purpose are Paris green and