POLYGONACE^E. PERSIC AKIA TRIBE. 537 



ORD. LXX. POLYGO^ACE^;. THE PERSICARIA 

 TRIBE. 



Flowers often bearing stamens only, or pistils only. 

 Perianth deeply 3 6 parted, often in two rows ; stamens 

 5 8 from the base of the perianth; ovary 1, not 

 attached to the perianth ; styles 2 or 3 ; fruit a flattened 

 or triangular nut. Herbaceous plants, distinguished by 

 the above characters and by bearing alternate leaves 

 furnished at the base with membranous stipules, which 

 encircle the stalk. The perianth is often coloured ; and 

 as the flowers, though not large, are numerous, and grow 

 in spikes or panicles, many of them are handsome plants. 

 Others, as the Dock, are unsightly weeds ; they are found 

 in all parts of the world, from the Tropics to the Poles. 

 The properties residing in the leaves and roots are very 

 different, the former being acid and astringent, and some- 

 times of an agreeable flavour ; the latter nauseous and 

 purgative. The powdered root of several species of 

 Rheum affords the valuable medicine Ehubarb, 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 Khubarb-stalks ; but the species mostly employed in 

 cookery is R. scutdta. To the genus Polygonum belong 

 P. Fagopyrum, Buck-wheat, or Beecli-wheat, so called 

 from the resemblance in shape between its seeds and the 

 mast of the Beech-tree. 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 afforded by its herbage ; and several other species 

 are used as medicine. Triplaris Americana attains the 

 dimensions of a tree, and is remarkable for being infested 



