HYSTEROPHYTA. 



499 



whether the Aristolochiaceas are related to the others ; they are by Eugler 

 united with Bafflesiaceje into one family, Aristulockiales. 



Order T. Aristolochiaceae. The majority are perennial 

 herbs or twining shrubs, whose stalked, simple, and generally more 

 or less cordate or reniform leaves are borne in 2 rows and are ex- 

 stipulate. The flowers are hermaphrodite, epigynous, regular or 

 zygomorphic ; perianth-leaves united, simple but most frequently 

 petaloid and 3-merous ; 6 or 12 (in Thottea as many as 36) stamens 

 with extrorse anthers. The ovary 

 is more or less completely 4-6- 

 locular with ovules attached in 

 the inner angles of the loculi 

 (Fig. 540 ]cf). The style is 

 short, and has a large, radiating 

 stigma (Fig. 540 ). Fruit a 

 capsule. Seeds rich in endo- 

 sperm. 



Asarum europasum. Each 

 shoot has 2 reniform foliage- 

 leaves, between which the ter- 

 minal flower is borne (the 

 rhizome becomes a sympodium 

 by development of the bud in 

 the axil of the upper foliage- 

 leaf). The flower is regular 

 and has a bell-shaped perianth 

 with 3 outer valv.ite, and 3 

 inner small segments (which 

 may be wanting). 12 (2 x 6) 

 free, extrorse stamens, 6 carpels. 

 Aristolochia dematitis (Birth- 

 wort) has an erect, unbranched 

 stem, bearing many flowers in 

 the leaf-axils, in a zig-zag row 

 (accessory buds in a unipared 

 scorpioid cyme). The flowers 

 are zygomorphic (Fig. 540), 

 formed by 3 alternating, 6-mer- 

 ous whorls. The perianth has 

 a lower, much-distended part (A-), succeeded by a narrow, bent 

 tube (r), which passes over into an oblique, almost tongue-like pro- 



FIG. 540. Flower of Aristolochia clematit is 

 (long. sect.). A Before pollination, and B 

 after: n stigma; a anthers; i an insect ; Itf 

 ovary. 



