merica, the aridity of which they are enabled to withstand in
consequence of the thickness of their skin and the paucity of evaporating
pores or stomata with which they are furnished,--these conditions not
permitting the moisture they contain to be carried off too rapidly; the
thick fleshy stems and branches contain a store of water. The succulent
fruits are not only edible but agreeable, and in fevers are freely
administered as a cooling drink. The Spanish Americans plant the Opuntias
around their houses, where they serve as impenetrable fences.

MELOCACTUS, the genus of melon-thistle or Turk's-cap cactuses, contains,
according to a recent estimate, about 90 species, which inhabit chiefly the
West Indies, Mexico and Brazil, a few extending into New Granada. The
typical species, _M. communis_, forms a succulent mass of roundish or ovate
form, from 1 ft. to 2 ft. high, the surface divided into numerous furrows
like the ribs of a melon, with projecting angles, which are set with a
regular series of stellated spines--each bundle consisting of about five
larger spines, accompanied by smaller but sharp bristles--and the tip of
the plant being surmounted by a cylindrical crown 3 to 5 in. high, composed
of reddish-brown, needle-like bristles, closely packed with cottony wool.
At the summit of this crown the small rosy-pink flowers are produced, half
protruding from the mass of wool, and these are succeeded by small red
berries. These strange plants usually grow in rocky places with little or
no earth to support them; and it is said that in times of drought the
cattle resort to them to allay their thirst, first ripping them up with
their horns and tearing off the outer skin, and then devouring the moist
succulent parts. The fruit, which has an agreeably acid flavour, is
frequently eaten in the West Indies. The _Melocacti_ are distinguished by
the distinct cephalium or crown which bears the flowers.

MAMMILLARIA.--This genus, which comprises nearly 300 species, mostly
Mexican, with a few Brazilian and West Indian, is called nipple cactus, and
consists of globular or cylindrical succulent plants, whose surface instead
of being cut up into ridges with alternate furrows, as in _Melocactus_, is
broken up into teat-like cylindrical or angular tubercles, spirally
arranged, and terminating in a radiating tuft of spines which spring from a
little woolly cushion. The flowers issue from between the mammillae,
towards the upper part of the