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 XI.
THE GENUS PILOCEREUS.
(From pilos, wool, and Cereus, in allusion to the long hairs on the spine cushions, and the affinity of the genus.)
NE 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 the late Mr. Bentham, sunk the genus under Cereus; but there are sufficiently good characters to justify us in retaining, for garden purposes, the name Pilocereus for the several distinct plants mentioned here. The botanist who founded the genus gives the following general description of its members: Stems tall, erect, thick, simple or branched, fleshy, ridged; the ridges regular, slightly tubercled, and placed closely together. Tubercles generally hairy, with bunches of short spines; the hairs long and white, especially about the apex of the stem, where they form a dense mass. Flowers on the extreme top of the matured stems, and arranged in a cluster as in the Melon Cactus, small, tubular; the petals united at the base, and the stamens attached to the whole face of the tube thus formed, expanding only at night, and fading in a few hours. These flowers have a disagreeable odour, not unlike that of boiled cabbage. Fruit fleshy, round, persistent, usually red when ripe. The species are natives of tropical America, and are generally found in rocky gorges or the steep declivities of mountainous regions.
Cultivation.—These plants require distinctly tropical treatment. During summer, they must have all the sunlight possible, and be supplied with plenty of water, both at the root and by means of the syringe. Air should be given on very hot days, but the plants should be encouraged to make all the growth possible before the approach of winter. In winter, they may be kept quite dry, and the temperature of the house where they stand should be maintained at about 60 degs., rising to 65 degs. or 70 degs. in the day. In March, the plants should be repotted into as small pots as convenient, employing a good, loamy soil and ample drainage. Should the hairs become soiled or dusty, the stems may be laid on their sides and then syringed with a mixture of soft soap and warm water, to be followed by a few syringefuls of pure water; this should cleanse the hairs and give them the white appearance to which the plants owe their attractiveness.