596 



SYSTEMATIC BOTANY. 



Fig. 969. 



Fig. 970. 



Fig. 971. 



Fig. 969. Flower of Great Bindweed {Calystegia 



septum) Fig. 970. Diagram of the flower, 



showing two bracts on the outside of the calyx, 

 &c Fig. 971. "Vertical section of the seed. 



Distribution, Sfc. — They are chiefly found in the plains and 

 valleys of hot and trojjical regions. A few occur in temperate 

 climates, but they are altogether absent in the coldest latitudes. 

 Examples : — Calystegia, Convolvulus, Exogonium, Ipomoea, 

 Batatas, Dichondra. There are 47 genera, and about 665 

 species. 



Properties and Uses. — They are chiefly remarkable for the 

 presence of an acrid milky purgative juice in their roots, hence 

 the order includes some important medicinal plants. The 

 purgative property of the juice is due to a peculiar resin. In 

 the roots of other species this resin is cither absent or in but 

 small quantity, and starch or sugar predominates, which renders 

 them edible. The seeds of some species are also purgative. 



Convolvulus, Bindweed From the incised fresh root of C. Scammonia, 



the valuable purgative gum-resin called Scammony is obtained. This plant 

 is a native of Asia Minor, Syria, the Levant, and Greece. The greater 

 part of the Scammony of English commerce is imported from Smyrna. The 

 roots of many other species also possess in a certain degree purgative proper- 

 ties ; as those of our native species, Convolvulus or Calj/s/eaia sepium. arverisis, 

 and Soldnnella,S(C. It is said that Convolvulus dissaiiis contains hydrocyanic 

 acid, and is one of the plants which is used for flavouring Noyau. 



Rhodorixa From the species of this genus the volatile oil called Oil of 



Ilhodium is said to be obtained. The powdered wood is used for snuff, and 

 for fumigation. 



F.TOfiouium pu7-^a This plant is a native of Mexico, near Chicanquiaco. 



Us tubercular roots constitute the true Jalap of the Materia Medica, so well 

 known as a purgative. 



//jowmvj. — The roots of T. Orizabensis are sometimes found intermixed with 

 true jalap. This spurious jalap is known in Mexico as male jalap, and in 

 Kn>^lish commerce as tcoody jalap or jalap trood, and on the Coniinent as 

 light or fusiform jalap. It possesses simil-<r, although less powerful properties 

 than those of true jalap. The roots of /. Turpctliuiu, Turpelb, were for- 

 merly much used as a j)urgative. The larpe roots of /. viacrorhiza contain 

 much farinaceous matter, and are eaten by the inhabitants of Georgia and Ca- 

 rolina. 



Ua'atas cdulis — The root of this plant constitutes the Sweet-Potato, which 

 is largely used as food in many tropical countries. 



