PHANEROGAMIA 



567 



unilocular, with a single basal ovule or with a free central placenta 

 bearing a number of ovules. 



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. 577). The 

 hermaphrodite flower is typically 

 trimerous, but a larger number 

 of members sometimes occurs in 

 the perigone or the androecium. 

 Ovary superior, formed of three 

 carpels, unilocular, with a single, 

 basal, atropous ovule. Fruit in 

 nearly all cases a triangular nutlet. 



GENERA. Rheum, Rhubarb. This is 

 an East Asiatic genus, with large, radical 

 leaves and a large, spreading, paniculate 

 inflorescence (Fig. 578). 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 chor- 

 isis ; P3+3, A6 + 3, G (3). Nectar for 

 visiting insects is secreted by the large 

 scales of the disc. The triangular ovary 

 becomes winged as it develops into the 

 fruit (Fig. 579). Species of Rheum are 

 cultivated 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 Polyyonum have a perigone 

 consisting of five, coloured leaves and a varying number of stamens. The triangular 

 fruits of Fayopyrum esculentum form Buckwheat (Fig. 508). 



OFFICIAL. The rhizome of Rheum officinale, Rh. palmatum, and probably other 

 species yields RADIX RHEI. 



Family 2. Chenopodiaeeae. Perennial or annual herbs, rarely 

 small woody plants, with alternate leaves. Flowers typically 

 pentamerous, with a single whorl in both perigone and androecium ; 

 P5, A5, G (2-5). Reduced, unisexual flowers are not infrequent. 



203 



FIG. 577. Leaf of Polygonum amplexlcaule showing 

 the ochrea (st). (J nat. size.) 



