O. Dillenii (Dillenius’); Fig. 79.—­An erect-growing, robust species, attaining a height of 15 ft., with flattened, ovate joints, about 5 in. long by 3 in. broad.  Cushions composed of short, white, hair-like bristles, and numerous long, stout, yellow spines.  Flowers yellow, tinged with red, 4 in. in diameter, freely produced on the ends of the youngest joints all summer.  Fruits similar to those of O. Ficus-indica.  A native of the West Indies, now naturalised in all warmer parts of the world.  In India it is so plentiful and widespread that Roxburgh, an Indian botanist, said it was a native.  In India, its fruits are eaten by the poor natives, and it is often planted as a hedge.  It is also a great pest in the open lands of that country, and large sums are annually expended in cutting it down and burying it.  This species, which requires warm greenhouse treatment, is also employed in the cultivation of cochineal.

[Illustration:  Fig. 79.  Opuntia dillenii.]

O. echinocarpa (spiny-fruited).—­A low, straggling shrub, not exceeding 11/2 ft. in height.  Joints cylindrical, from 1 in. to 3 in. long, less than 1 in. thick.  Cushions of rather coarse bristles and numerous spines, from 1/2 in. to 1 in. in length.  Flowers 2 in. in diameter, yellow, produced in summer.  Fruit short, depressed, almost saucer-shaped, and bearing spines nearly 1 in. long.  A native of Colorado, &c.  It requires stove treatment.  The variety major has stems 4 ft. high, joints 8 in. to 10 in. long, and long, sheathed spines.  This species is closely related to O. Bigelovii and O. Davisii.

O. Emoryi (Emory’s).—­A prostrate, spreading plant, less than 11/2 ft. high.  Joints cylindrical, curved, 4 in. long, 11/2 in. thick.  Tubercles very prominent, longitudinally attached to the stem, the apices crowned with pea-shaped cushions of short bristles, and numerous radiating spines, some of which are fully 2 in. long, very strong and needle-like.  Flowers 21/2 in. in diameter, sulphur-yellow, tinged with purple, produced in August and September.  Fruit 21/2 in. long and 1 in. thick, covered with cushions of bristles and spines.  A native of Mexico, on dry, sandy soils, where its prostrate stems, clothed with powerful spines, form a hiding-place for the small animals, snakes, &c.  Stove or warm greenhouse treatment is best for this species.

O. Engelmanni (Engelmann’s).—­A stout, coarse-looking plant, 6 ft. high, with woody stems and large, flat, green joints, 1 ft. long and 9 in. in diameter.  Cushions 11/2 in. apart, composed of coarse bristles, and one or two spines over 1 in. long, and pointing downwards.  Flowers 3 in. in diameter, yellow, produced in May and June.  Fruit nearly round, 2 in. long, purplish both in rind and pulp, the latter rather nauseous to the taste.  Mexico.  This is a greenhouse plant which grows freely and flowers annually under cultivation.  It is very similar to O. monacantha, a much better known species.  According to American botanists, it is probably the most widely spread of the whole Cactus tribe.