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—­hence the specific name.  The stoutest spines are 3 in. long, and are sharp and strong as needles.  This species (which is probably a native of Mexico) is deserving of a place in collections of Cactuses because of the character of its spines.  Probably it is only a variety of O. Tuna.  It requires warm-house treatment.

O. hystricina (porcupine-like).—­This beautiful species was discovered in the San Francisco Mountains mixed with O. missouriensis, to which it is nearly allied.  It is spreading in habit, the joints 3 in. to 4 in. long and broad; cushions 1/2 in. apart, rather large, with numerous spines, varying in length from 1/2 in. to 4 in., and short, yellowish bristles.  Flowers large, yellow.  Fruit 1 in., long, spiny.  This plant is not known in English collections, but it is described by American botanists as being attractive and a free grower.  As it is found along with O. missouriensis, it ought to prove hardy in England.

O. leptocaulis (slender-stemmed).—­This little Mexican species is chiefly remarkable for its fragile, numerous, twig-like joints, thickly dotted with tubercles and numerous spirally-arranged cushions of reddish bristles, with long, grey spines.  It does not flower under cultivation.  Requires stove treatment.

O. leucotricha (white-haired).—­An erect-stemmed kind, with flattened joints, ovate or oblong in shape, and bearing numerous cushions, 1/2 in. apart, of short bristles, with a large, central spine, and a few others rather shorter.  When young these spines are rigid and needle-like; but as they get older they increase in length, and become soft, and curled like stiff, white hair.  Young plants are noticeable for their small, subulate leaves of a bright red colour, whilst old examples are almost as interesting as the Old Man Cactus (Pilocereus senilis), the long, white, hair-like spines of the Opuntia hanging from the older