ridges of the stem.  Generally, the flowers are about as long as wide, and the ovary is covered with scales or modified sepals.  The fruit is succulent, or sometimes dry, and, when ripe, is covered with the persistent calyx scales, often surrounded with wool, and usually bearing upon the top the remains of the withered flower.  The position of the flowers is on the young part of the stem, usually being perched in the centre, never on the old part, as in some of the Cereuses.  The flowers open only under the influence of bright sunlight, generally closing soon after it leaves them.

The geographical distribution of the species, of which over 200 have been described, extends from Texas and California to Peru and Brazil; they are in greatest abundance in Mexico, whence most of the garden kinds have been introduced.  The conditions under which they grow naturally vary considerably in regard to temperature and soil; but they are all found in greatest numbers and most robust health where the soil is gravelly or sandy, and even where there is no proper soil at all, the roots finding nourishment in the clefts or crevices of the rocks.  As a rule, the temperature in the lands where they are native is very high during summer, and falls to the other extreme in winter, some of the species being found even where frost and snow are frequent; the majority of them, however, require what we would call stove treatment.

Turning now to a consideration of those kinds known as garden plants, we find that comparatively few of the species known to botanists are represented in English collections, though, perhaps, we may safely say that not one of the kinds known would be considered unworthy of cultivation except by those who despise Cactuses of whatever kind.  Their flowers are conspicuous both in size and brilliancy of colour; and in the curious, grotesque, and even beautifully symmetrical shapes of their stems, one finds attractions of no ordinary kind.  The stem of E. Visnaga shown at Fig. 48 may be taken as an instance of this—­apart from the cluster of star-like, bright yellow flowers seen nestling upon the top of their spine-protected dwelling, the whole suggesting a nest of young birds.  This plant is indeed one of the most remarkable of the Echinocactuses, owing to the size and number of its spines—­which are 3 in. long, almost as firm as steel, and are used by the Mexicans as toothpicks—­and to the gigantic size and great weight of the stem.  The following account of a large specimen of this species introduced to Kew in 1845, is taken from an article from the pen of the late Sir Wm. Hooker in the Gardeners’ Chronicle of that year.  This gigantic plant was presented to the nation, in other words to Kew, by F. Staines, Esq., of San Luis Potosi.  Such was its striking appearance, that it was stated that, if exhibited in the Egyptian Hall, Piccadilly, some hundreds of pounds might be realised by it.  In a letter from Mr. Staines, here quoted, our readers will perceive