YAM. 
YACK. See Ox. 
YAM,—botanically Deoscorea. A genus of ex- 
otic, tuberous-rooted, monocotyledonous plants, 
constituting the type and the main bulk of the 
natural order Dioscoree or Dioscoreacee. The 
characteristics of this order, which readily dis- 
tinguish its plants from all other endogens, are a 
large fleshy root, a climbing stem, cordate or an- 
gular leaves, and inconspicuous and for the most 
part greenish or yellowish flowers. About forty 
species of it have been introduced to Britain; and 
all these, excepting five or six, belong to the ge- 
nus dioscorea; and about twenty other species 
of that genusare known. ‘Two of the dioscoreas 
in Britain are hardy, one is suited to the green- 
house, and all the others require the heat and 
protection of the stove; a few have a height of 
about 3 or 4 feet, and most of the others have 
a height of from 8 or 10 to 20 or 25 feet; three 
have -divided leaves, four have lobed leaves, two 
have oblong leaves, and the others have cor- 
date leaves; four or five have whitish or reddish 
flowers, and most of the others have green or 
yellowish flowers ; one has an ornamental appear- 
ance, six or seven are agricultural or culinary, 
and the rest are interesting only to botanists; a 
few love a soil of sandy peat or of peaty loam, 
the rest love a soil of rich mould, and all are 
propagated by division of the tuberous roots, 
more or less in the manner of potatoes. All the 
interesting and useful kinds, unhappily, belong 
to the stove, and develope their economical value 
only or chiefly in tropical countries. 
The common or cultivated yam, Dioscorea sa- 
tiva, grows wild in the woods of Ceylon and Mala- 
bar, and is supposed to have been artificially intro- 
duced thence to the West Indies, and is diffused 
as a cultivated plant over a large portion of the 
tropical countries of the world, and was intro- 
duced as a botanical curiosity from the West In- 
dies to Britain in 1733. Several varieties of it 
occur wild; and many varieties are in cultiva- 
tion. The root of one of the most common is as 
large as a man’s leg, of an irregular form, dirty 
brown on the outside, and white and meally 
within ; the stems of all are triangular and 
winged, and either trail on the ground when 
they have no support, or climb to a comparatively 
great height, some so high as 20 or 25 feet, when 
they grow in the immediate vicinity of trees ; 
the leaves are cordate, and have each two ears 
somewhat like those of arum; and the flowers 
have a greenish colour, and bloom in August. 
The roots of this plant constitute one of the most 
important articles of ordinary food in tropical 
Iy. 
YARD. 785 
/ 
countries ; and are preferred by many persons, 
whether Indians or Europeans, to potatoes; and 
they are cooked and used in a variety of ways, 
both in substance and when ground into a sort 
of flour, the solid roots being suitable alike for 
boiling and for roasting, and the flour serving 
alike for puddings and for bread. Radical cut- 
tings or sets, each containing an eye or bud, are 
planted in a manner similar to the sets of pota- 
toes; each cutting usually produces 3 or 4 large 
roots; and in America, the crop is commonly 6 
or 8 months in the ground before the roots are 
taken up for use. In British horticulture, a cut- 
ting or set may be planted in a pot of fresh rich 
mould, the pot plunged in a hotbed of tan, anda 
little water given till the shoot appears above the 
surface ; and in this way a plant may be obtained 
of 10 feet or so in height, but without any con- 
siderable sized roots. 
The prickly-stemmed yam, Dioscorea aculeata, 
is a native of India, and was introduced thence 
to the hothouses of Britain in 1803. Its roots 
are esculent and delicate, similar in taste to fine 
dry choice ones of the common yam, yet some- 
what similar in appearance to those of the bat- 
tatas ; its stems naturally attain a height of about 
10 or 12 feet; and its leaves are cordate and 
somewhat similar to those of the common yam. 
—The wing-stalked yam, Dzoscorea alata, was in- 
troduced from India to Britain in 1739. Its root 
is much eaten in Malacca and Java; its stems 
naturally attain a height of about 15 or 16 feet; 
and its leaves are cordate, and its flowers green. 
—The bulb-bearing yam, Dioscorea bulbifera, is 
one of the longest known kinds, and was intro- 
duced to Britain in 1692; its stems attain a 
height of 12 or 14 feet; and its flowers are green 
and bloom in July and August.—The Brazilian 
yam, Dioscorea brasiliensis, was introduced to Bri- 
tain from Brazil in 1823. Its roots are esculent ; 
its stems rise to the height of about 8 feet; and 
its leaves are lobed.—The five-leaved yam, Dzos- 
corea pentaphylla, is a native of India, and is there 
called the wild yam, and was introduced thence 
to Britain in 1768. Its roots are esculent, yet 
previous to preparation contain much acrimony ; 
its stems attain a height of about 10 feet; and 
its leaves are divided and quinquefoliate. 
YARD. A court. See Farm-Yarp. 
YARD. A measure. See Mrasurus. 
YARD MANURE. See Farm-Yarp Manoure. 
YARD OF LAND. An old provincial super- 
ficial measure, of very variable extent, amounting 
in some counties to 15 acres, in others to twenty, 
and in others to twenty-four, thirty, or thirty-four. 
3D 
