MANUAL OF NATUKAL HISTORY. 497 



usually trifid ; stigmas three ; fruit a glo- 

 bular berry ; embryo very small, albuminous. 

 Occur chiefly in temperate and tropical parts 

 of Asia and America. This family yields the 

 different kinds of Sarsaparilla, many of which 

 are much employed in medical practice ; 

 though possessed of valuable properties in 

 their native places, they seem to be much 

 impaired by exportation, and in Europe to 

 have but feeble actions. 



II. SUB-CLASS. — Unisexual-Dictyogens (Dianthise). 



Male and female organs on separate flowers. 



1. Family. — Yams (Dioscoreacese). Shrubs, twin- 



ing, tuberous ; leaves mostly alternate ; flowers 

 small, spiked, bracteated ; perianth 6-divided, 

 adherent ; stamens six ; anthers introrse ; 

 ovary adherent, 3 -celled ; ovules anatropal ; 

 style 2-3-fid ; stigmas undivided ; fruit cap- 

 sular, compressed, trilocular ; seeds winged or 

 wingless ; embryo small, albuminous. Mostly 

 inhabitants of tropical countries. Chiefly 

 valuable as affording yams, the tropical sub- 

 stitute for the potato : in Europe, this family 

 is represented by the Black Bryony (Tamus 

 communis). 



2. Family. — Tail-worts (Triuridacese). Herbs, pe- 



rennial ; rhizome creeping ; leaves solitary ; 

 flowers regular, with 1 -flowered, bracteate 

 stalks ; perianth free, corolline, 3-6- partite, 

 permanent ; stamens 3-6 (?) ; anthers ex- 



