ming the fleshy
stems. These are extremely various in character and form, being globose,
cylindrical, columnar or flattened into leafy expansions or thick
joint-like divisions, the surface being either ribbed like a melon, or
developed into nipple-like protuberances, or variously angular, but in the
greater number of the species furnished copiously with tufts of horny
spines, some of which are exceedingly keen and powerful. These tufts show
the position of buds, of which, however, comparatively few are developed.
The stems are in most cases leafless, using the term in a popular sense;
the leaves, if present at all, being generally reduced to minute scales. In
one genus, however, _Peireskia_, the stems are less succulent, and the
leaves, though rather fleshy, are developed in the usual form. The flowers
are frequently large and showy, and are generally attractive from their
high colouring. In one group, represented by _Cereus_, they consist of a
tube, more or less elongated, on the outer surface of which, towards the
base, are developed small and at first inconspicuous scales, which
gradually increase in size upwards, and at length become crowded, numerous
and petaloid, forming a funnel-shaped blossom, the beauty of which is much
enhanced by the multitude of conspicuous stamens which with the pistil
occupy the centre. In another group, represented by _Opuntia_ (fig. 1), the
flowers are rotate, that is to say, the long tube is replaced by a very
short one. At the base of the tube, in both groups, the ovary becomes
developed into a fleshy (often edible) fruit, that produced by the
_Opuntia_ being known as the prickly pear or Indian fig.

The principal modern genera are grouped by the differences in the
flower-tube just explained. Those with long-tubed flowers comprise the
genera _Melocactus_, _Mammillaria_, _Echinocactus_, _Cereus_, _Pilocereus_,
_Echinopsis_, _Phyllocactus_, _Epiphyllum_, &c.; while those with
short-tubed flowers are _Rhipsalis_, _Opuntia_, _Peireskia_, and one or two
of minor importance. Cactaceae belong almost entirely to the New World; but
some of the Opuntias have been so long distributed over certain parts of
Europe, especially on the shores of the Mediterranean and the volcanic soil
of Italy, that they appear in some places to have taken possession of the
soil, and to be distinguished with difficulty from the aboriginal
vegetation. The habitats which they affect are the hot, dry regions of
tropical A