specimens may be obtained by
making the most of this fact. One of the crested or monstrous forms,
when grafted on a flat-stemmed kind, presents the queerest of
appearances, looking like a large green cockscomb growing out of the top
of a bladdery kind of stem. Equally odd combinations may be made by
grafting a flat-stemmed kind on one whose stem is cylindrical. As all
the kinds unite with the greatest ease, a taste for oddities among
plants may easily be gratified by making use of Opuntias in this way.
The time most favourable for the operation is spring-say, the month of
April. For full information on how to graft Cactuses, see Chapter IV.,
on Propagation.

SPECIES.

O. arborescens (tree-like).--This species is known as the Walking-Stick
or Elk-Horn Cactus, from its cylindrical, woody stems being made into
very curious-looking walking-sticks (examples of which may be seen in
the Museum at Kew), whilst the arrangement of the branches is suggestive
of elk horns. Habit erect; joints cylindrical, branching freely, and
forming trees from 8 ft. to 30 ft. high. Stems covered with oblong
tubercles and tufts of long, needle-like spines, which give the plant a
very ferocious aspect. Flowers on the ends of the young branches, 2 in.
to 3 in. in diameter, bright purple in colour, developing in June. It is
a native of Mexico, &c., and requires greenhouse or stove treatment. The
skeletons of this species, as seen scattered over the desert places
where it is wild, have a very singular and startling appearance. They
stand in the form of trees, quite devoid of leaves, spines, or flesh,
and, owing to the peculiar arrangement of the ligneous layers, nothing
remains except a hollow cylinder, perforated with mesh-like holes,
indicating the points where the tubercles and small branches had been.
These skeletons are said to stand many years.

O. arbuscula (small tree).--Another of the cylindrical kinds, with a
solid, woody trunk, about 4 in. through, and clothed with smooth, green
bark; it grows to a height of 7 ft. or 8 ft. Branches very numerous,
slender, copiously jointed, the ultimate joints about 3 in. long and 1/2 in.
thick; they are slightly tuberculated, and bear tufts of spines nearly
1 in. long. Flowers 11/2 in. in diameter, produced in June; petals few,
greenish-yellow, tinged with red. It is a native of Mexico, and requires
stove treatment. A pretty plant, or, rather, a very remarkable one, even
when not in flower, the thin br