bare porous rocks.

[Illustration: FIG. 54. MELOCACTUS COMMUNIS.]

M. depressus (flattened); Bot. Mag. 3691.--Stem broader than high,
deeply cut into about ten broad furrows, along the sharp angles of which
are clusters of pale brown spines, from 1/2 in. to 1 in. long, arranged in a
star, each cluster 1 in. apart. Instead of the cylinder-like cap of the
Turk's-Cap species, this one has a short, broad tuft of white wool and
red spines, like a skull-cap. The flowers are small, and soon wither,
but remain attached to the oblong berries, which stand erect in a dense
cluster in the centre of the cap, and are of a delicate rose-colour. The
first introduced plant of this was sent home by Mr. Gardner, who
introduced the Epiphyllums and other Cactuses. It flowered on the way to
England, and matured its seeds soon after its arrival. It is a native of
Pernambuco.

M. Miquelii (Miquel's); Fig. 55.--This species appears to have been
introduced in 1838, when two plants of it were sent from the West Indian
Island, St. Croix, to the Hamburg Botanic Gardens. The stem is oval,
dark green, with fourteen well-defined ribs, as regular as if they had
been carved with a knife. The spine-tufts are small; spines short,
black-brown, about nine in each tuft, one of which is central, the
others radiating; they are less than 1/2 in. long. The "cap" is cylindrical,
3 in. high by 4 in. in diameter, and composed of layers of snow-white
threads, mixed with short reddish bristles.

[Illustration: FIG. 55. MELOCACTUS MIQUELII.]

These three are the only species of Melocactus that have become known in
English gardens, although various other kinds, named M. Lehmanni, M.
Zuccarini, M. Ellemeetii, M. Schlumbergerianus, &c., occur in books.

CHAPTER X.

THE GENUS PILOCEREUS.

(From pilos, wool, and Cereus, in allusion to the long hairs on the
spine cushions, and the affinity of the genus.)

One of the most striking plants in this order is the "Old Man Cactus,"
botanically known as Pilocereus senilis, which is the only member of
this genus that has become at all known in English gardens. In
Continental gardens, however, more than a dozen species are to be found
in collections of succulent plants; and of these one of the most
remarkable is that represented at Fig. 56. The limits of the genus
Pilocereus are not definitely fixed, different botanists holding
different views with respect to the generic characters. Recent writers,
and among them