XXVII. — THE BLACK BRYONY. 
Tarn us communis Linne. 
T WINING and climbing plants of all kinds are far more abundant in the dense 
vegetation of Equatorial regions than they are in our Temperate Zone. The 
small Family of the Yams, named, from the somewhat shadowy early herbalist, 
Dioscoreace* e, is mainly southern, tropical, or extra-tropical, and but scantily 
represented in the north. The acrid starchy tubers of several species of Dioscorea, 
mostly natives of the Old World Tropics, are well-known articles of food and have 
been introduced into the West Indies. By cultivation, or at least on being cooked, 
these Yams lose their original acridity. One species, D. pyrenaica Bubani, occurs 
in the Pyrenees, an interesting relic apparently of the northward Post-Glacial 
migration ; but otherwise the Family is only represented in Europe by the two 
species of the genus Tamus. Another remarkable species, Testudinaria Elepliantipes 
Salisbury, the Hottentot Bread, which can be seen in most Botanical Gardens, is a 
native of South Africa, and produces an enormous tuber rising above the ground 
and covered by a thick tessellated cork, from which, during the rainy season, arises 
a slender climbing stem. These tuberous structures by which these plants hibernate 
or sstivate — pass through, that is, the season unfavourable to vegetation, whether 
that season be a cold winter or a dry summer — are of varied morphological nature. 
In Testudinaria it is the first internode of the stem that is thus enlarged : in Tamus 
it is a lateral outgrowth of the first two internodes, which forms a large, fleshy, 
ovoid, but entirely subterranean mass. This is externally black and thus, no doubt, 
gained for this genus the name of Black Bryony, as distinguished from the white 
tubers of Biyonia dioica Jacquin, a plant in no way related to Tamus , although the 
two often grow side by side. 
From this tuber, in our hedgerows, in spring, the rapidly-growing slender 
twining stem may be seen to develop, growing to a length of several yards in the 
single season of its existence and sometimes branching, but from the first dependent 
upon some support round which it can twine. It is angular in section, but has none 
of the roughness of the Hop or the dense woolliness of the White Bryony. 
It is to this rapidity of growth that the name Bryony, the Greek /3puama, 
bruonia , from fipva), bruo , to shoot, refers ; but the origin of Gesner’s name Tamus , 
or rafher of Pliny’s name Uva taminia for the fruit— a name which lingers in the 
Italian tamaro — is unknown. Elongation taking place apparently intermittently on the 
many sides of the apical shoot, brings about the circumnutation or nodding movement 
described by Darwin, in which the slender apex swings round from its older portion 
once in two and a half to three hours. This takes place in a constant direction, 
which in the Dioscoreace # is, as traced from below upwards, the direction in which 
the hands of a clock travel, i.e. from right to left, or sinistrorse , a direction which is, 
perhaps, less common among twining stems than the dextrorse , or counter-clockwise , 
twist. 
