The "old man" cactus is one of the curiosities of plant life. Cereus or Piloeereus senilis, derives both its botanical and popular names from the large number of long silvery white hairs which cover the upper portion of its stem, and impart a peculiar resemblance to the hoary head of an aged man. These hairs are really soft weak spines, which attain the length of several inches, and instead of spreading regularly, or projecting rigidly, as in other members of the family, they are flaccid and pendulous, thickly clothing the stem. It is necessary to protect this plant from dust if it be desired to preserve its beauty, for it has a very disreputable and unwholesome appearance when what should be silvery white hairs become dingy and stained. It is, therefore, preferably grown in a small glass case, where with a few other select cactuses it will be seen to excellent advantage. Though C. senilis is one of the best known species in small collections, yet large plants are seldom seen, and probably the finest in England is that grown at the Oxford Botanic Garden. This is sixteen feet high, of proportionate diameter, and has been in cultivation at least a hundred years, having been originally imported by the Duke of Bedford, and transferred at the dispersal of the unique Woburn collection to Oxford. Even this height is said to be exceeded in its native home of Mexico, where specimens have been described as reaching the height of twenty feet.

One character common in varying degrees to all the cactuses, but very strongly developed in the "old man" cactuses, is the large quantity of calcium oxalate secreted in the cells of the stem. To such a degree are these crystals formed, that old stems, when cut, lose the succulent portion of their structure but still preserve their form, becoming almost like petrified stems, solid, heavy and stone-like. - Lewis Castle.