PETALOIDE 209 
THE BLACK BRYONY GROUP. 
Thisis the group (family Dioscoracez) to which the 
Yam belongs. The order contains about one hundred 
and seventy species included in nine genera which 
are found in warm, temperate and tropical regions, 
especially America. 
They are either shrubs with a fleshy tuberous root 
or rhizome, or are climbing or trailing plants; the 
stems are herbaceous, and the plants twine to the 
left. 
There is but one genus in the British Isles of this 
order, Tamus or Black Bryony. This is extremely 
acrid and the berries poisonous. Dioscorea affords 
tubers which are.used for food, as ‘*‘ Yam,”’ cultivated 
like the Potato. It isa twining plant and is propped 
up like Hops on poles. The tubers are farinaceous, 
white and mealy, but they are acrid and poisonous 
unless cooked, when they are nutritious. The other 
genus, Testudinaria, is employed in the same way. 
A characteristic of this order is the dicecious 
character of the flowers, and other points are the 
adherent calyx and corolla, the three-celled ovary, 
six stamens, numerous-seeded berry and consolidated 
_carpels. 
The twining habit is characteristic, the plants 
requiring the support of a hedge to grow properly. 
The root-stock is black and fleshy, and may be used 
in place of Bryonia for mandrake occasionally. The 
stem is terete and glabrous, with alternate net-veined 
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