[Illustration:  Fig. 35.—­Echinocactus Haynii.]

E. hexaedrophorus (tubercles six-sided); Fig. 36.—­This plant is distinguished by the gouty-looking tubercles into which its broad, spiral ridges are divided, and which look as if they would suddenly burst like a blister if pricked with a pin.  It grows about 4 in. in height, and is similar in form to what is shown in the accompanying figure, except that the top is usually flatter than here represented.  The whole stem has a glaucous hue, and the spines are reddish-brown.  The flowers, which are produced freely in June and July, are short-tubed, spreading to a width of 2 in.; the petals toothed at the tips, and arranged in several rows, overlapping each other, the colour being white, tinted with rose, with a disk-like cluster of yellow stamens in the centre, and a white-rayed stigma.  A native of North Mexico, introduced about 1830.  It is very slow-growing, attaining full size in not less than six years from seed; indeed, it is stated that in twelve years a plant of it did not grow more than 2 in.  Still, slow as it is, it remains in good health when kept in a sunny position on a shelf in a greenhouse or in a dwelling-room, so that it may be recommended for places where space is very limited.  Like E. gibbosus, it does best when grafted on to another kind.  We have seen perfect “drum-sticks” formed by grafting a full-grown plant of this on the stem of a Cereus.

[Illustration:  Fig. 36.—­Echinocactus hexaedrophorus.] E. horizonthalonis (spreading-spined); Fig. 37.—­Stem globose, usually flattened on the top, and divided into eight or nine large ribs or ridges, grey-green in colour.  Spines in crowded star-shaped clusters along the apex of the ribs, seven spines in each cluster, all of them strong, slightly curved, horn-like, and marked with numerous rings; they are yellow, tipped with red when young, ash-coloured when old; the longest are about 2 in. in length.  Flowers terminal, springing from the young spine tufts, each 4 in. across, with two rows of petals arranged regularly in the form of a cup; colour deep rose, paler on the inside of the cup; stamens very numerous, with white filaments and yellow anthers.  The flowers expand at sunrise and close again in the evening, each one lasting about a week; they are very agreeably scented.  Flowering season, May and June.  The plant is a native of Mexico, and was introduced in 1838. (Syns.  E. equitans, E. horizontalis.)

[Illustration:  Fig. 37.—­Echinocactus horizonthalonis.]

E. Le Contei (Le Conte’s); Fig. 38.—­Another of the large-stemmed kinds, which have only recently found their way into English gardens, although long since discovered and described by American travellers.  The illustration represents a young plant.  When full-grown, this species has a stem 5 ft. high by 2 ft. wide, with broad deep channels and ridges, wrinkled and covered with a thick network of stout spines, which