POLYGONUM. CX. POLYGONACE^E. 473 



sports into many pleasing varieties with yellow and white, red and wnite, red 

 and yellow flowers. June Sept. 



2. M. DICHOTOMA. Mexican Four-o'clock. Fls. sessile, erect, axillary, soli- 

 tary. 1\. From Mexico. Stem 2f high, dichotomous, with yellow flowers, 

 opening at 4 o'clock like the former. July, Aug. 



3. M. LONGIFLORA. Long-flowered Four-o'clock. Lvs. pubescent ; fls. crowd- 

 ed ; tube of the cal. very long. 7J. Native of Mexico. Stem 2f high. Tube of 

 the calyx slender, hairy, twice as long as the leaves. Flowers white. Jn. Sept. 



ORDER CX. POLYGONACE^. BUCKWHEATS. 



Herbs, rarely shrubs, with alternate leaves. ' [base of the leaf-stalks ; occasionally 0. 



Slip, of that remarkable kind called ochreae, cohering round the stem in the form 01 a sheath above the 



Fls. mostly perfect, and in racemes. 



Cal. Sepals united at base, imbricate in aestivation. 



Sta. definite, inserted on the calyx near the base. 



Ova. free, with a single erect ovule. Styles or stigmas several. 



Fr. Achenium usually triangular. 



Sils. Embryo generally on one side of farinaceous albumen. 



Genera 29, species 490, widely diffused throughout the world. 



Properties. -The roots of these plants are nauseous and purgative. Rhubarb of the shops is the root 

 of some unknown species of this order, native of Tartary. But the leaves and stalks of sorrel, the gar- 

 den rhubarb, &c., are agreeably tart, and contain oxalic acid ; the petioles of the latter, together with the 

 farinaceous seeds of the buck- wheat, are well-known articles of food. 

 Conspectus of the Genera. 



$ 6. Stigmas 3, multifid. 3 outer sepals smaller. .... Rumex. 4 



( 6. Stamens \ 9. Stigmas multifid Rticum. 1 



t < mostly 5, united at base, persistent and enclosing the fruit Polygonum. 3 



Sepals ( 4. Radical leaves reniform, on long petioles Oxyria. 2 



1. RHEUM. 



Rha, the river Volga, on whose banks the plants are said to be native. 



Calyx colored, 6-sepaled, persistent; stamens 9 ; styles 3 ; stigmas 

 multifid, reflexed ; achenia 3-angled, the angles margined. % Fls. 

 fasciculate, in racemose panicles. 



R. RHAPONTICUM. Garden Rhubarb or Pie-plant. Lvs. smooth, cordate- 

 ovate, obtuse; petioles channeled above, rounded at the edges. Native of Asia, 

 cultivated in gardens for the sake of the juicy, acid petioles. These are taken 

 in a green state, in the spring of the year, and made into tarts and pies, whose 

 excellence is well known to every one. Stem stout and fleshy, 3 4f high, 

 hollow, with large, sheathing stipules at the joints. Leaves very large, 1 2f 

 long, f as widej on petioles of nearly the same length. Panicle terminal, at 

 first enclosed in a white, membranous bract which at length bursts, disclosing 

 innumerable greenish- white flowers. May. 



2. OXYRIA. R. Br. 



Gr. o|uj , acid ; in allusion to the qualities of its leaves. 



Cal. 4-sepaled,2 inner sepals largest ; achenium 3-sided, with abroad, 

 membranaceous margin ; sta. 2 6 ; styles 2, stigmas large, plumose. 

 ^ Lvs. mostly radical^ petiolate. ' Stem nearly leafless^ paniculate-racemose. 

 O. RENIPORMIS. Hook. (Rumex digynus. Linn.} Mountain Sorrel. 

 Radical Ivs. reniform, on long petioles; outer sepals oblong, half as long as 

 the inner, valvular sepals; stamens 2; styles 2. Found on the summits of the 

 White Mts., in moist ravines, and N. to the Arc. Sea. The plant is acid to the 

 taste, like Rumex acetosus. Stem 3 4' in height. June. 



3. POLYGONUM. 



Gr. TroXuf, many, yopv, knee ; that is, plants with many joints. 



Sepals 4 6, mostly 5, connected at base, colored or corolla-like, 

 persistent ; sta. 5 9, mostly 8 ; sty. 2 3, mostly 3, short, filiform ; 

 ach. mostly triangular, usually covered by the persistent calyx. 

 Herbaceous. Sts. jointed. Fls. in axillary and terminal fascicles and 

 ipiltes or paniculate racemes. 



