524 PART IV. CLASSIFICATION. 



Rheum, the Rhubarb, has six (three internal and three external) 

 perianth-leaves and two whorls of stamens, the outer containing six, and 

 the inner three; Rheum undulatum and other species are cultivated. 

 Rumex. the Dock, has flowers of similar structure, but the inner Avhorl of 

 stamens is absent ; the triquetrous fruits are completely enveloped by the 

 inner whorl of perianth-leaves (Fig. 337 C c) ; the leaves contain a large 

 quantity of oxalic acid. Polygonum has usually five petaloid perianth- 

 leaves and a varying number of stamens (5-8) ; P. Fagopyrum, the Buck- 

 wheat, is cultivated for the sake of its mealy seeds. 



Cohort IV. Asarales. Affinities doubtful. Flowers mono- 

 clinous or unisexual : ovary inferior : ovules numerous. 



Order 1. ARISTOLOCHIACELE. Flowers 3-6-merous, monoclinous : 

 perianth of three connate petaloid segments forming a three-lobed 

 tube : stamens 6 or 12, with extrorse anthers : ovary usually 

 G-locular, with numerous ovules in two longitudinal rows along the 

 inner angles of each loculus. The 

 minute embryo is enclosed in the 

 copious endosperm. They are herbs 

 or shrubs, often climbing, with large 

 leaves. 



In Asarum europceuni (Asarabacca) the 

 three lobes of the perianth are equal : 

 alternating with them are three scales 

 which probably represent a corolla : the 

 twelve stamens (apparently in two whorls) 

 are free, and the connective is produced 

 Fio. 333. - Asarum ouropamm. (FJ 33^ The &nnual shoots of tfae c 

 Longitudinal section of the flower , ,, , 



(maK.); P perianth. (After Sachs.) in S stem ^ar four cataphyllary leaves, 

 two large petiolate reniform foliage-leaves, 



and a terminal flower. The lateral branches spring from the axils of the 

 uppermost foliage-leaf and of the scales. In Aristolochia, the Birthwort 

 (see Fig. 243, p. 412), the limb of the perianth is obliquely lipped ; the six 

 anthers are sessile and adnate to the short style (see p. 462). A. Sipho is 

 a climber frequently cultivated : A. Clematitis, though not indigenous, is 

 found wild in Britain, generally on ruins ; the flowers of the latter occur 

 usually several together in the axils of the leaves, and those of the former 

 in pairs, one above the other, together with a branch, in the axils of the 

 leaves of the shoot of the previous year. 



Cohort V. Santalales. Parasitic plants : leaves, when 

 present, entire : stamens equal in number to the leaves of the 

 perianth and superposed upon them : ovary inferior, uuilocular ; 

 ovules usually devoid of integument. 



Order 1. SAXTALACEJE. Parasites provided with chlorophyll : 



