MLOCEKEOS. 63 



.some of the Mamillarias, has long formidable spines, and bears dark roae- 

 <;oloured flowers. E. phienieeus, E. pauciflorus, E. chloranthus, and E, virij- 

 diflorus are also curious forms. One very distinct variety in Mr. Boiler's 

 collection must not be omitted — namely, B. peotinatus rufispinaa, -which haj 

 numerous neat brown spines, and bright shining rose-coloured flowers 

 3 inches in diameter, 



PiLOCEEEUS.— The " Old Man" Cactus is one of the ourioBities of 

 plant life which always attract attention, and its appearance is certainly 

 sufficiently strange to excite some surprise. Pilocereus 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. 

 As was remarked, however, in the case of the Mamillarias, 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 P. senilis is one 

 «f 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 16 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 20 feet. One character common in 

 varying degrees to all the Caotese, but very strongly developed in the 

 " Old Man " Cactus, 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. Examples of this kind can be seen in the museums at 

 Kew, the whole centre of the stem being filled with lime crystals. 



Several other species are in cultivation in botanic gardens and a few 

 collections, perhaps the best known being P. Celsianus, which has ex- 

 tremely fine hairs closely pressed to the surface of the stem, and having 

 a cobweb-like appearance ; very distinct from P. senilis. There is also 

 one dwarf-growing rare species, named P. chrysomallus, which has 

 golden spines. The Pilocereus very rarely flower in cultivation, though 



