248 MONOCHLAMYDE7E 



flavour, the latter nauseous and purgative. The powdered root 

 of several species of Rheum affords the valuable medicine, Rhubarb, 

 and the leaf-stalks of the same plants are much used for making 

 tarts ; the sharp taste is attributed to the presence of oxalic, nitric, 

 and malic acids. Two native kinds of Sorrel, and several of Dock, 

 belong to the genus, Rumex. Sorrel [R. acetosa) is sometimes used 

 in the same way as Rhubarb-stalks, but the species mostly em- 

 ployed in cookery is R. sctUala. To the genus Polygonum belongs 

 P. fagopyrum, Buck-wheat. In some countries the flour derived 

 from its seeds is made into bread, but in England it is not much 

 cultivated, except as food for pheasants, which are very partial 

 to it. P. tinctorum is extensively cultivated in France and Flanders 

 for the sake of the blue dye aiforded by its herbage, and several 

 other species are used in medicine. Triplaris Americana attains 

 the dimensions of a tree, and is remarkable for being infested by 

 ants, which excavate dwellings for themselves in the trunk and 

 branches, 



1. Polygonum (Persicaria). — Perianth deeply 5-cleft, not falling 

 off ; stamens 5-8 ; styles 2 or 3 ; fruit, a triangular or flattened 

 nut. (Name in Greek signifying having many knees, or joints, 

 from the numerous joints of the stem.) 



2. Rumex (Dock). — Perianth deeply 6-cleft, in two rows, the 

 interior segments large ; stamens 6 ; styles 3 ; fruit, a triangular 

 nut, covered by an enlarged inner perianth. (Name, the Latin 

 name of the plant.) 



3. OxYKiA (Mountain Sorrel). — Perianth deeply 4-cleft, in two 

 rows, the interior segments large ; stamens 6 ; styles 2 ; fruit, a 

 flattened nut with a membranous wing. (Name from the Greek, 

 oxys, sharp, from the acid flavour of the stem and leaves.) 



I. Polygonum {Persicaria) 



1. P. aviculare (Common Knot-grass). — Stem branched, 1-2 feet 

 long, prostrate, or, when growing with tall plants, erect ; leaves 

 narrow, elliptical, small ; floit'ers in axillary clusters of 2-5 ; styles 

 3 ; fruit triangular. A common weed, with leaves which are 

 furnished with white chaft'y stipules, and with minute flesh-coloured 

 or greeni.sh-white flowers. Varies greatly in size. Waste ground 

 and roadsides ; abundant. — Fl. all the summer. Annual. 



2. P. maritimum (Sea Knot-grass). — A variable plant, distin- 

 guished by its large-nerved stipules and long shining fruits, which 

 project from the perianth ; stems shrubby, thicker than in the last ; 

 leaves usually thicker, and glaucous ; and floicers also larger. 

 South coast. — Fl. August, September. Perennial. 



