E. pectiniferus (comb-bearing); Bot.  Mag. 4190.—­One of the most striking of the plants of this genus, owing to the character of its stem, and the large size and beauty of its flowers.  The former resembles a pear with the thin end downwards; its height is from 4 in. to 6 in., and it has about twenty ridges, which are sharply defined and bear along their angles little cushions of white wool 1/2 in. apart, with a radiating cluster of brown spines springing from each.  The arrangement of the spines in rows is not unlike the teeth of a comb.  The flowers are borne near the top of the stem, and consist of a green, fleshy tube, clothed with spines and little tufts of white wool; the sepals form a row beneath the petals, and are yellowish, tinged with purple; petals 2 in. long, broad, with the upper margins toothed and the tip acute, their colour being bright rose, tinged with greenish-white at the base; stamens yellow; stigma large, green.  The form of the flowers is that of a cup, nearly 3 in. across.  Introduced from Mexico in 1845.  Flowering season, April and May.  It requires warm-house treatment.

E. polycephalus (many-headed); Fig. 42.—­Stem globose when young, becoming cylindrical with age; number of ribs varying from twelve to twenty, sharply defined, and bearing, at intervals of 1 in., clusters of stout, reddish spines, somewhat flattened on the upper side, and marked with raised rings, or, as it is termed, annulated, the central ones attaining a length of over 3 in. on old plants, and sometimes curved.  The flowers are enveloped at the base in a dense mass of white wool, which hides the tube, its spines only showing through; petals narrow, 1 in. long, spreading like a saucer, and coloured bright yellow; stamens numerous, yellow, as also is the large rayed stigma.  California and Colorado, on stony and gravelly hills.  Flowers in spring; introduced to Kew in 1886.  This new plant is remarkable in that it is often found wild with as many as twenty to thirty stems or heads springing from the same base, and even young plants show early a disposition to develop several heads.  The largest stems are from 11/2 ft. to 21/2 ft. high, and have a somewhat forbidding appearance, owing to the size and strength of their numerous spines.  For its cultivation, a warm-house temperature appears most suitable; it bears a close resemblance to E. texensis.

[Illustration:  Fig. 42.—­Ridge, with spines, of Echinocactus polycephalus.]

E. Pottsii (Potts’).—­The stem of this is shown in Fig. 43.  Full-sized plants are 11/2 ft. in diameter, and have about a dozen ridges with acute sinuses, the ridges being rounded and even.  The spines are 1 in. long, bristle-like, and are arranged in clusters of seven or nine, with a cushion of white wool at the base of each cluster.  Flowers short-tubed, about 2 in. across, and coloured yellow; they are produced on the top of the stem in summer, several expanding