joints in much the same manner as they do from the upper part of the stem of the Pilocereus.  Flowers yellow, produced in June.  This species is a native of Mexico, and requires stove treatment.  Seeds of this, and, indeed, of a large proportion of the cultivated Opuntias, may be procured from seedsmen, and as they germinate quickly, and soon produce handsome little plants, a collection of Opuntias is thus very easily obtained.

O. macrocentra (large-spurred).—­A flat-jointed species, growing to a height of 3 ft.; the joints large, almost circular, thinly compressed, and usually purplish in colour.  Cushions about 1 in. apart, with spines often 3 in. long, of a greyish colour, and generally pointing downwards.  Flowers 3 in. across, bright yellow; they are developed in May and June, on the upper edges of the youngest joints.  This plant is a native of Mexico; it is at present rare, but the unusual colour of the joints, its compact, freely-branched habit, the extraordinary length of its spines, and the size of its flowers, ought to win for it many admirers.  It is easily grown if kept in an intermediate house.  Plants of it may be seen in the Kew collection.

O. macrorhiza (large-rooted); Figs. 82, 83.—­In this Texan species we have a combination of the principal characters for which the genus Opuntia is remarkable:  The thick, fleshy roots, which are a supposed source of food, and which look like potatoes; the cylinder-shaped older stems, and the flattened, battledore-like joints; the tufts of bristles on the stems, and deciduous, longer spines on the joints; the large, beautiful, yellow flowers; and the small leaves on the newly-formed joints.  In habit and flowers this kind resembles O. Rafinesquii; and if not quite hardy in England, it is nevertheless sufficiently so to thrive in any sunny position where it would be protected from frost and excessive wet.  The accompanying illustrations represent the characters of this species so well that further description is not needed.  The flowers are developed in early summer.

[Illustration:  Fig. 82.  Flowering branches of opuntia macrorhiza.]

[Illustration:  Fig. 83.  Roots of opuntia macrorhiza.]

O. microdasys (small, thick).—­This is a handsome little Mexican plant.  Its flattened joints, which are nearly circular in outline, are thickly covered with little cushions of bright orange-yellow bristles, the cushions being so close together that the short bristles almost hide the green joints from view.  The stems are semi-decumbent, and they branch somewhat freely.  Flowers not seen.  It thrives in a warm greenhouse temperature.  The best examples of this pretty Opuntia are grafted on a robust-growing kind, the stock being about 1 ft. long, and the scion forming a compact head of pretty, healthy-looking joints.  Treated in this way, this species is most interesting and attractive.  It may also be grown on its own roots.  There is a variety of it, named rufida, in which the bristles are reddish-brown.