d is remarkable for the depressed form
of its stem, which may be likened to a sea urchin, both in size and
shape. Old plants are from 6 in. to 8 in. in diameter, and about 4 in.
high; the spiral formed by the tubercles rises very gradually, and each
of the latter is surmounted by a tuft of strong, brown, radiating
spines, imbedded in a little cushion of wool. The flowers spring from
the outside of the depressed top of the stem, two or three opening
together and forming a beautiful picture, both as to size and colour.
The tube is short and green, with a row of long green sepals at the top,
and above these the petals, which are 2 in. long, overlapping, recurved,
the edges toothed, and the colour a brilliant cinnabar-red. The stamens
are in two series, very numerous, and the anthers are bright yellow.
Looking at the flattened, spiny stem, it seems impossible that such
large, handsome flowers should be produced by it. A native of Bolivia;
introduced about 1846. It blossoms in July, and may be grown on a shelf
in a cool greenhouse, as advised for the E. centeterius.

E. concinnus (neat); Fig. 29.--A small species with a globose stem,
2 in. high and 3 in. wide, and about twenty ridges, which are rounded,
rather broad, each bearing about half-a-dozen little bunches of spines
arranged in a star. The flowers are numerous, as large as, or larger
than, the stem, being 3 in. long and broad, the tube covered with brown
hair-like spines, and having a few reddish scales, whilst the petals are
in several rows, overlapping, with pointed tips, and are coloured dark
yellow with a red streak down the centre. Several flowers are sometimes
developed together on a little stem, when they have the appearance of
being much too large for so small a plant to support. The pale green of
the stem and its brown spines contrast prettily with the handsome yellow
flowers, which are brightened by the streaks of red on the petals and
the clear red colour of the stigma. It is a native of Mexico, and was
introduced about 1840, flowering early in summer. It requires a warm
greenhouse temperature all the year round, with, of course, plenty of
sunshine. It may be grafted on the stem of an erect-growing Cereus, such
as C. serpentinus or C. Napoleonis, the stock to be not higher than
6 in., and about as wide as the plant of E. concinnus is at the base.

[Illustration: FIG. 29.--ECHINOCACTUS CONCINNUS.]

E. coptonogonus (wavy-ribbed); Fig. 30.--Stem globose, seld