PETALOIDE^;. 369 



tuberous roots contain much starch. This is extracted (by washing 

 the roots of Tacca pinnatifida) by the inhabitants of Tahiti and other 

 islands of the South Sea, who use the meal for bread, cultivating the 

 plant in fields. This species, and T. dubia, montana, and others, are 

 used in like manner in Malacca, the Moluccas, Cochin China, &c., and 

 are sometimes eaten raw with an acid, which neutralizes the acridity. 

 Genera : Tacca, Forst. ; Ataccia, Presl. 



BIOS CO RE AC E/E (YAMS) are plants with twining stems rising from 

 large tuberous or knotted woody root-stocks, with broad netted-veined 

 stalked leaves, small dioecions 6-androus regular flowers, the tube of the 

 6-parted perianth adhering in the fertile flowers to the 3-celled ovarv ; 

 styles 3, distinct or deeply trifid ; ovules 1-2 in a cell ; stamens of the 

 barren flower 6, on the perianth; fruit a 3-celled (or by suppression 

 1-celled) dehiscent capsule, or a succulent berry ; seeds with a small embryo 

 in a cavity in the hard perisperin. Illustrative Genera : Tamus, L. ; Dios- 

 corea, L. 



Affinities, &c. Very near to Smilacese, from which they differ in the in- 

 ferior ovary and the cavity in the perisperm ; the mostly capsular fruit is 

 replaced by a berry in Tamus, like that of Smilax, but inferior instead of 

 superior. The epigynous condition relates these plants to Amarylhdacese. 

 Some authors consider they are related to Aristolochiaceae ; but it is a 

 distant affinity. 



Distribution. A rather large group, chiefly tropical ; Tamils communis 

 is British. 



Qualities and Uses. The sap is often more or less acrid ; but the 

 tubers formed by certain species of Yams (Dioscorea sativa, alata, and 

 aculeatd) contain abundance of starch ; so that under cultivation, and after 

 cooking, when the noxious principle is dissipated, they become valuable 

 articles of food. The tubers of other Dioscorece are unfit for food ; and 

 those of Tamus communis, Black Bryony, have acrid, purgative, and emetic 

 properties. Testudinaria elephantipes, a Cape plant, in cultivation in our 

 Botanic gardens, produces a remarkable tuberous growth, resembling a 

 >rugged stump of an old tree, covered by a kind of false bark, which is tes- 

 sellated with large compound angular facets ; its internal substance is eaten 

 by the Hottentots. 



OECHIDACEJE. ORCHIDS. 

 Coh. Orchidales, Hook. 



Diagnosis. Herbs, distinguished by their irregular flowers, 

 6-merous perianth in separate at the base from the ovary ; stamen 

 (1, or very rarely 2) gynandrous, pollen cohering in waxy or mealy 

 masses ; ovary inferior, placentas parietal. 



Character. 



Perianth mostly petaloid, adherent, in two circles ; the outer circle 

 of three pieces (sepals), distinct or more or less coherent below, 



