in. apart, composed of a little
tuft of white woolly hair, a cluster of erect, rather long bristles,
like a small shaving-brush, and all pointing upwards; spines usually
only one in each cushion, and this is slender, deflexed, white, and from
1 in. to 2 in. long. Sometimes the joints are wholly spineless. Flowers
21/2 in. in diameter, purplish, very handsome, produced in May and June.
Fruit not known. The roots of this species bear tubers often 1 in. in
thickness, and several inches in length, and these tubers will grow into
plants if severed and planted. It requires stove treatment. Native
country, Mexico.

[Illustration: FIG. 81. OPUNTIA FILIPENDULA.]

O. frutescens (shrubby).--A thin-stemmed, copiously-branched species.
Joints almost continuous, like ordinary branches, from 2 in. to 6 in.
long, the thickest not exceeding 1/4 in. Cushions on raised points or
tubercles, each consisting of a small tuft of hair, inclosed in a row of
bristles, and one long, central spine, often exceeding 2 in. in length.
When young, the spines are inclosed in a thin, bony sheath. Flowers
scattered along the younger branches, 1 in. across, greenish-yellow,
borne in June. Fruit 1 in. long, pear-shaped, smooth, scarlet, with tufts
of bristles all over it, and a depression in the apex. Mexico. This
forms an interesting pot-plant when properly cultivated. It should be
grown in a warm greenhouse.

O. Grahami (Graham's).--This is one of several species of Opuntia which
are remarkable in having thick, fleshy roots, not unlike those of the
Dahlia. The joints are 2 in. long and 1 in. in diameter, cylindrical, with
adpressed tubercles, 1/2 in. or more long, each tubercle bearing a tuft of
long, straight, radiating spines. Flowers 2 in. across, yellow, borne on
the ends of the ripened joints in June. Fruits 11/2 in. long and 3/4 in. wide,
covered with stellate clusters of short, bristle-like spines. This plant
is a native of Mexico, and is a recent introduction. From the nature of
its roots, which are no doubt intended to serve as reservoirs for times
of extreme drought, it should be grown in well-drained, sandy soil, and
kept quite dry all winter. It requires stove treatment.

O. horrida (horrid).--An erect, stout-stemmed plant, with flattened,
green joints, about 5 in. long by 3 in. wide. Cushions 1 in. apart,
composed of short, reddish bristles, and long, tawny red spines, about
eight in each cushion, and of a peculiarly ferocious appearance--