armless 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,
most likely, is found in the smaller kinds when wild. Under artificial
cultivation there are, however, many conditions more or less
unfavourable to the health of plants, and, in the case of Cactuses, very
large specimens, when imported from their native haunts to be placed in
our glass houses, soon perish. At Kew, there have been, at various
times, very fine specimens of some of the largest-growing ones, but they
have never lived longer than a year or so, always gradually shrinking in
size till, finally, owing to the absence of proper nourishment, and to
other untoward conditions, they have broken down and rotted. This
rotting of the tissue, or flesh, of these plants is the great enemy to
their cultivation in England. When it appears, it should be carefully
cut out with a sharp knife, and exposed to the influence of a perfectly
dry atmosphere for a few days till the wound has dried, when the plant
should be potted in a sandy compost and treated as for cuttings.
Sometimes the decay begins in the side of the stem of the plant, in
which case it should be c