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Dioscoreaceae (Very ornamental-leaved)

Very ornamental-leaved (with few exceptions) stove herbaceous climbers, with large tuberous roots, admirably adapted as trellis or pillar plants. Flowers whitish or yellowish, inconspicuous. Leaves broad, cordate, or angular. In the winter months, Dioscoreas should be kept in a cool (but not cold) place, either in the pots or in some perfectly dry sand. The most suitable soil is a rich light compost, formed of turfy loam and well-decomposed manure, in about equal parts. They should have abundance of root room, and be liberally supplied with water during the growing season, gradually diminishing the quantity as the shoots show signs of decay. Propagated by divisions of the tubers, which may be effected either in autumn or spring, while they are at rest, but never when growing. D. Anoectochilus (Anoectochilus-like). l. deep olive-green, beautifully marbled with gold, with a central band of the same colour, broadly acuminate; when young, they are of a uniform plain bright green. South America, 1865. D. argyraea (silvery). l. green, cordate, about 5in. across, seven-nerved; nerves bordered with distinct irregular angular patches of silvery-grey. Columbia.

D. Batatas (Batatas).* Chinese Yam. fl. white, dioecious, very small, in axillary racemes, generally sterile. l. deep green, very glossy, opposite, cordate, acuminate. Stems annual, smooth, green or purplish, sometimes attaining a height of from 6ft. to 9ft. The roots are used like potatoes-boiled, roasted, and cooked in various other ways. Probably the great depth to which the tubers descend, and the consequent expense of harvesting the crop, has prevented this useful hardy vegetable from being much cultivated in this country.

D. bulbifera (bulb-bearing).* fl. greenish, disposed in gracefully drooping racemes. l. broad, cordate. East Indies, 1692. A very old inhabitant of our stoves, and at one time strongly recommended as a substitute for the potato. (G. C. n. s., viii. 48.) D. Decaisneana (Decaisne's). Decaisne's Yam. l. very light green, opposite or alternate, deeply cordate at base, regularly narrowed to the apex. Tubers in some cases smooth and regularly shaped, as in some varieties of potato, others very irregular. China, 1862. Perhaps this is a variety of D. Batatas, from which it, however, differs a good deal in the tubers not being developed at such a great depth underground.

D. discolor (two-coloured). l. beautifully mottled with two or three shades of green, large, cordate; under surface rich purplish-rimson. Tropical America. D. illustrata (illuminated). l. satiny-green, marked by fine transverse whitish parallel lines between the nerves, with an irregular central band of silvery-grey, and a few angular patches of the same colour, generally placed in juxtaposition with the ribs; about 6in. long. produced at the base into two bluntish lobes; under surface purple. Brazil, 1873. (G. C. 1873, 1730.) D. multicolor (many-coloured).* l. rich green, beautifully spotted and variegated with pale spots and blotches, most numerous near the principal veins; cordate, 3in. to 5in. long, and 2 1/2in. to 3in. wide; under surface pale lurid purple. Rio Negro, 1868. (I. H. 1871, 53.) There are about half-a-dozen varieties of this species known, of which the following are in cultivation: chrysophylla, leaves olive-brown, variegated with yellow; Eldorado, leaves satiny-green, with silvery-grey central band, and irregular blotches of the same colour; melanoleuca, leaves deep green, with central silvery band and silvery blotches along the veins; metallica, leaves bronzy, with coppery central band.

D. nobilis (noble). l. velvety-bronze, variegated with yellow. Brazil, 1868. D. retusa (retuse). fl. dull yellowish; racemes axillary, slender, pendulous, many-flowered. l. alternate, loosely scattered, digitate; leaflets five to seven, petiolulate. South Africa, 1870. (G. C. 1881, xv. 511.) D. sativa (cultivated). Common cultivated Yam. l. alternate, cordate, round, ovate, cuspidate; lobes of base close together. Stem smooth, round, slender. West Indies, 1733.

D. vittata (striped). l. flushed with claret-colour beneath, or variegated with red and white on both sides, large, cordate. (B. M. 6409.)