DIV. n 



ANGIOSPERMAE 



621 



Order 6. Polygoninae 



Family 1. Polygonaceae. For the most part perennial herbs, with hollow 

 stems swollen at the nodes, and alternate, simple leaves. The membranous 

 stipules of the latter are coherent to form a 

 sheath or OCHREA protecting the terminal bud ; 

 when broken through by the growth of the stem, 

 this remains as a tubular sheath around the lower 

 part of the internode (Fig. 617). 



Mainly natives of the N. Temperate zone. 



GENERA. Rheum, Rhubarb. This is an East 

 Asiatic genus, with large, radical leaves and a large, 

 spreading, paniculate inflorescence. Leaves simple, 

 cordate-reniform, with palmate venation, sometimes 

 more or less lobed. *The flower has a perigone of 

 two similar whorls, and two whorls of stamens, the 

 outer whorl being double by chorisis ; P3 + 3, 

 A 6 + 3, G (3). Nectar for visiting insects is 

 secreted by The large scales of the disc. The tri- 

 angular ovary becomes winged as it develops into 

 the fruit (Fig. 618). Species of Rheum are culti- 

 vated as ornamental plants and as vegetables. 

 Rumex acetosa, Sorrel, with sagittate leaves. The 

 structure of the flowers of the hermaphrodite 

 species of Rumex is similar to that of Rheum, but 

 the inner whorl of stamens is wanting. The 

 species of Polygonum have a perigone consisting 

 of five coloured leaves and a varying number of 

 stamens. The triangular fruits of Fagopyrum 

 esculentum form Buckwheat (Fig. 571 B}. 



OFFICIAL. The Rhizome of Rheum officinale, Rh. palmatum, and probably 

 other species yields EADIX RHEI. 



FIG. 617. Leaf of Polygonumamplexi- 

 caule showing the ochrea, st. 

 (J nat. size.) 



FIG. 618. Rheum officiwlc. A, Flower: ti, the same cut through longitudinally; C, gynaeceuin 



with disc. 



nn: D, fruit. (After LURSSEN, magnified.) 



Order 7. Piperinae 

 Single family. Piperaceae. The genus Piper is important. Flowers as a rule 



