CONTOLVULACE^E. 



461 



956. The order is characterised generally by the presence of an 

 acrid juice in the roots, which has purgative properties. On this 

 account several of the plants are used medicinally. The old genus Can- 

 volvulus has been split into various genera; such as Ipomcea, Exogonium, 

 Pharbitis, Batatas, Qwmoclit, Calonyction, and Lepistemon, according 



to the form of the corolla, the exsertion or inclusion of the stamens, 

 the form and nature of the stigma, and the structure of the ovary. 

 Exogonium Purga (Ipomcea Purga, or Convolvulus Jalapd) is the 

 Jalap plant, a native of Mexico, which grows well in this country, re- 

 quiring only the protection of a frame during winter. The plant has 

 flowered regularly for many years in a cold frame in the Edinburgh 

 Botanical Garden. The root-stock is the officinal part. It has a 



Figs. 652-659. Organs of fructification of Convolvulus (Calystegia) sepium, to illustrate the 

 natural order Convolvulacese. 



Fig. 652. Diagram of the flower, showing two bracts, five unequal divisions of the imbricated 

 calyx, five lobes of the plicate corolla, five stamens alternating with the corolliiie lobes, and a 

 quadrilocular ovary. 



Fig. 653. Flower bud. 6, Large bracts, c, Calyx, p, Corolla. 



Fig. 654. Vertical section of the lower part of the flower. 6, Bracts, f, Calyx, p, Tube of 

 eorofla, bearing the filaments of the stamens, e. o, Ovary. *, Style. 



Fig. 655. Summit of the style and stigmas. 



Fig. 656. Fruit, /, surrounded by the calyx, c, and the bracts, 6, which are persistent. 



Fig. 657. Seed. h. Hilum. 



Fig. 658. Section of the seed showing the corrugated cotyledons. 



Fig. 659. Embryo separated. 



