arge,
spreading masses under favourable conditions. Joints broad, flattened,
obovate, about 4 in. long by 2 in. wide, light green; spine-cushions less
than 1 in. apart, and composed of numerous small, white spines, with from
one to four longer ones; these latter fall away when the joints get old.
Leaves very short, with a little wool about their bases. Flowers 3 in. in
diameter, appearing from May onwards; petals yellow, dashed with rose,
sometimes wholly rose-coloured or brick-red. Stamens deep red; pistil
yellow, with a conical stigma. Fruit nearly round, spiny, about 2 in.
long. A native of Wisconsin, and westward to the San Francisco
Mountains; introduced in 1814. This species is as hardy as O.
Rafinesquii, and thrives under similar treatment. It has stood 22 degs.
of frost without suffering, requiring only protection from rain in
winter. In North America it forms large, spreading masses on gravelly
hillsides, and is much dreaded by travellers, and especially by horses;
there it is usually covered with snow from Christmas to the following
May.

O. monacantha (one-spined).--A tall, robust plant, not unlike O.
Dillenii in general habit. It has flat, large joints, oblong or ovate in
outline, rather thinly compressed, and bearing grey cushions over 1 in.
apart, with a solitary spine, 11/2 in. long, springing from the centre of
each cushion, and pointing downwards. Flowers sulphur-yellow, 21/2 in.
across, borne on the last-ripened joints in May, and abundant on
well-grown plants. Fruits ovate, 2 in. long, green, with tufts of short,
brown bristles; pulp edible. The species is a native of Brazil, but is
now common in many tropical and sub-tropical countries. It is a
free-growing kind, soon forming a large specimen if planted in a bed of
old brick-rubble, or other light, well-drained soil, and kept in warm
greenhouse temperature.

O. nigricans (blackish); Bot. Mag. 1557.--Stem stout, erect, becoming
hard and woody when old. Joints flat, oval in outline, 5 in. to 8 in. long.
Cushions 11/2 in. apart, composed of short reddish-brown bristles and two
or three long stout spines, which are yellow when young, but almost
black when ripe. Flowers produced on the young, ripened joints,
orange-red, about 3 in. across and developed in August and September.
Fruit pear-shaped, rich crimson when ripe. Introduced from Brazil in
1795. This well-marked species thrives in a warm greenhouse. It branches
freely, and has a healthy aspect at a