recommended, and also by not properly mixing the oil with the soap and
water; and the amateur cannot, therefore, be too careful in his use of
this excellent insecticide. It would be easy to recommend other
insecticides, so called, for Cactuses; but whilst they are less
dangerous to the plants, they are often as harmless as pure water to the
insects.

For scale, which sometimes infests these plants, and which is sometimes
found upon them when wild, the paraffin may be used with good effect.

Thrips attack Phyllocactus, Rhipsalis, and Epiphyllum, especially when
the plants are grown in less shade, or in a higher temperature, than is
good for them. Fumigation with tobacco, dipping in a strong solution of
tobacco, or sponging with a mixture of soap and water, are either of
them effectual when applied to plants infested with thrips. The same may
be said of green-fly, which sometimes attacks the Epiphyllums.

A blight, something similar to mealy bug, now and again appears on the
roots of some of the varieties of Echinocactus and Cereus. This may be
destroyed by dipping the whole of the roots in the mixture recommended
for the stems when infested by mealy bug, and afterwards allowing them
to stand for a few minutes immersed in pure water. They may then be
placed where they will dry quickly, and finally, in a day or two,
repotted into new compost, first removing every particle of the old soil
from the roots.

Diseases.--When wild and favourably situated as regards heat and
moisture, the larger kinds of Cactus are said to live to a great age,
some of the tree kinds, according to Humboldt, bearing about them signs
of having existed several hundred years. The same remarkable longevity,