D1OON 



DIOSMA 



487 



lanugindsum, Hort., is a very woolly kind. Gt. 48, pp. 

 154, 155. A variable species. D, tomentdsum, once sold 

 by Pitcher and Manda, was probably woollier than the 

 type. D. spinuldsnm, Dyer, dift'ers mainly in having the 

 segments margined with small sharp points. Mex. A.F. 

 7:461. W . M . 



DIOSCOREA (Dioscorides, the Greek naturalist). 

 Dioscoreacete. The type genus of a small family (of 

 about 8 genera) allied to Liliaceee. It contains upwards 

 of 150 widely dispersed and confused species, most of 

 them native to tropical regions. Stems herbaceous and 

 twining or long-procumbent, usually from a large tuber- 

 ous root, and sometimes bearing tubers in the axils. 

 Lvs. broad, ribbed and netted-veined, petiolate, alternate 

 or opposite, sometimes compound. Dioecious. Fls. 

 small; calyx 6-parted, anthers 6; styles 3, ovary 3-loculed 

 and calyx adherent to it. Fr. a 3-winged capsule. Seeds 

 winged. The great subterranean tubers of some species 

 are eaten in the manner of potatoes. For an inquiry into 

 the prehistoric cultivation of Dioscoreas in America, 

 see Gray & Trumbull, Amer. Journ. Sci. 25:250. 



A. Stems strongly winged. 



alata, Linn. Fig. 714. Stem 4-winged or angular: Ivs. 

 opposite, cordate-oblong or cordate-ovate, with a deep, 

 basal sinus, glabrous, devoid of pellucid dots, 7- 

 nerved ( sometimes 9-nerved) , with the outer pair united : 

 staminate spikes compound, special ones whorled, short, 

 flexuose : pistillate spikes simple : fls. distant, anthers 

 subglobose, about as long as the filament : capsule 

 leathery, elliptical. India and the S. Sea Islands. 

 Widely cult, in the tropics under many vernacular 

 names. Tubers reach a length of 6-8 ft., and some- 

 times weigh 100 Ibs. ; edible. The roots continue to 

 ijrow for years. Variable. 



714. Dioscorea alata. 

 Showing foliage (X K) and a small tuber. 



AA. Stems terete (cylindrical). 



B. Lvs. plain green. 



divaricata, Blanco. (D. Batatas, Decne.). YAM. CHI- 

 NESE YAM. CHINESE POTATO. CINNAMON VINE. Very tall 

 climbing (10-30 ft.), the Ivs. 7-9 ribbed, cordate-ovate 

 and shining, short-petioled, bearing small clusters of 

 cinnamon-scented white fls. in the axils: root tubers 



deep in the ground, 2-3 ft. long, usually larger at the 

 Lower end. Philippines. F.S. 10:971. R.H. 1854, p. 

 247, 451-2. This is often grown in the tropics for its 

 edible tubers, which, however, are difficult to dig. In 

 this country the word Yam is commonly applied to a 

 tribe of sweet potatoes (see Sweet Potato). The Yam 

 is hardy. The root will remain in the ground over 

 winter in New York, and send up handsome tall, twining 

 shoots in the spring. The plant bears little tubers in 

 the leaf-axils, and these are usually planted to produce 

 the Cinnamon Vine; but it is not until the second year 

 that plants grown from these tubercles produce the 

 large or full grown Yams. A form with short and potato- 

 like tubers is D. Decnism'fimi, Carr. (R.H. 1865:110). 



715. Air Potato ^Erial tuber of Dioscorea bulbifera (X 



bulbil era, Linn. AIR POTATO. Fig. 715. Tall-climbing: 

 Ivs. alternate, cordate-ovate and cuspidate, 7-9-nerved, 

 the stalks longer than the blade : fls. in long, lax, droop- 

 ing, axillary racemes. Tropical Asia. G.C. II. 18:49. 

 Somewhat cult. S. as an oddity and for the very large 

 angular axillary tubers ( which vary greatly in size and 

 shape. ) These tubers sometimes weigh several pounds. 

 They are palatable and potato-like in flavor. The root 

 tubers are usually small or even none. 



villdsa, Linn. Stems slender, from knotted rootstocks : 

 Ivs. cordate-ovate, cuspidate-attenuate, 9-11-ribbed, 

 somewhat pubescent or downy beneath, alternate, oppo- 

 site or whorled: fls. greenish, the staminate in drooping 

 panicles, the pistillate in drooping, simple racemes: cap- 

 sules very strongly winged. Common in thickets from 

 N. Eng. to Fla. Perennial. Twining 8-10 or even 15 ft. 

 Offered in the trade as a hardy border and arbor plant. 



BB. Lvs. variously marked and colored, at least beneath. 



discolor, Hort. Lvs. large, cordate -ovate, cuspidate, 

 with several shades of green, white-banded along the 

 midrib and purplish beneath : fls. greenish and incon- 

 spicuous: root tuberous. S. Amer. Lowe 54. Useful 

 for the conservatory. Suggestive of Cissus discolor. 



multicolor, Lind. & Andre". Probably only a form of 

 the last: Ivs. variously marked and blotched and veined 

 with silvery white, red, green and salmon. S. Amer. 

 I.H. 18:53. Very decorative glasshouse plant. 



Other species are cult, in the Gulf region. One, with 2- 

 winged stem and 3-lobed Ivs. (the "Yampie"), is perhaps D. 

 triloba, Linn. One with prickly cylindrical stems and opposite 

 oblong-ovate Ivs. may be D. nummuldria, Lam. 



D. satlva, Linn., was founded upon a number of tropical cul- 

 tivated species, and the name should be dropped. For Japanese 

 cultivated species, see Georgeson, A.G. 13:80, with illustrations. 



L. H. B. 



DI6SMA (Greek, divine odor). Rutacece. Small, ten- 

 der, heath-like shrubs from southwestern Africa. Of 

 the 228 species described, barely a dozen now remain in 

 this genus, the rest being mostly referred to allied 

 genera, especially Adenandra, Agathosma and Barosma. 

 Lvs. alternate or opposite, linear-acute, channeled, ser- 

 rulate or sometimes ciliate, glandular dotted: fls. white 

 or reddish, terminal, subsolitary or corymbose, pedicel- 

 late ; calyx 5-parted; hypogynous disk, 5-sinuate, 5- 

 plaited; petals 5; style short ; stigma capitate. Latest 

 monograph in Flora Capensis, vol. 1 ( 1859-60) . "W". ]. 



Diosma ericoides is more or less well known in 

 America, and is put to various uses in floral decora- 

 tions, in spray, or branchlets cut to the required length, 

 and stuck in formal designs as a setting for other flow- 



