n, in the
Cactuses themselves we have curious cases of plant mimicry; as, for
instance, the Rhipsalis, which looks like a bunch of Mistletoe, and the
Pereskia, the leaves and habit of which are more like what belong to,
say, the Gooseberry family than to a form of Cactus. From this it will
be seen that although these plants are almost all succulent, and
curiously formed, they are by no means singular in this respect.

The characters of the order are thus defined by botanists: Cactuses are
either herbs, shrubs, or trees, with soft flesh and copious watery
juice. Root woody, branching, with soft bark. Stem branching or simple,
round, angular, channelled, winged, flattened, or cylindrical; sometimes
clothed with numerous tufts of spines which vary in texture, size, and
form very considerably; or, when spineless, the stems bear numerous
dot-like scars, termed areoles. Leaves very minute, or entirely absent,
falling off very early, except in the Pereskia and several of the
Opuntias, in which they are large, fleshy, and persistent. Flowers
solitary, except in the Pereskia, and borne on the top or side of the
stem; they are composed of numerous parts or segments; the sepals and
petals are not easily distinguished from each other; the calyx tube is
joined to, or combined, with the ovary, and is often covered with
scale-like sepals and hairs or spines; the calyx is sometimes partly
united so as to form a tube, and the petals are spread in regular
whorls, except in the Epiphyllum. Stamens many, springing from the side
of the tube or throat of the calyx, sometimes joined to the petals,
generally equal in length; anthers small and oblong. Ovary smooth, or
covered with scales and spines, or woolly, one-celled; style simple,
filiform or cylindrical, with a stigma of two or more spreading rays,
upon which are small papillae. Fruit pulpy, smooth, scaly, or spiny, the
pulp soft and juicy, sweet or acid, and full of numerous small, usually
black, seeds.

Tribe I.--Calyx tube produced beyond the Ovary. Stem covered with
Tubercles, or Ribs, bearing Spines.

1. MELOCACTUS. Stem globose; flowers in a dense cap-like head, composed
of layers of bristly wool and slender spines, amongst which the small
flowers are developed. The cap is persistent, and increases annually
with the stem.

2. MAMILLARIA. Stems short, usually globose, and covered with tubercles
or mammae, rarely ridged, the apex bearing spiny cushions; flowers
mostly in rings ro