316 POPULAR ECONOMIC BOTANY. 



There are two distinct varieties in ordinary commerce, known 

 as East Indian and Turkey, but there are others in the 

 market; properly the East Indian should be called Hi- 

 malayan, and the Turkey Russian; there are besides the 

 Dutch trimmed, Chinese, English, and French. The species 

 of Rheum supposed to yield them are R. undulatum, R. 

 palmatum, R. compactum, and R. Rhaponticum. About 140 

 tons is the annual supply. The roots are cut into pieces of 

 various size and shape, but usually of the bulk of an orange ; 

 the outer bark is peeled off, and the lumps are apparently 

 trimmed with a file; very often they are perforated with 

 large holes, which have been made for the purpose of 

 stringing them up to dry. 



Jalap. — The dried tubers of Exogonium Purga (Nat. 

 Ord. Convolvulacea). (Plate XVII. fig. 89.) 



This valuable medicine has been known in Europe ever 

 since 1733, when it was introduced from Mexico, its native 

 place, by Dr. Houston ; it derives its name from a place named 

 Xalapa, where it is most abundant. Until lately it was sup- 

 posed to be derived from a species of Convolvulus, which, 

 under the name of C. Jalapa, has long been cultivated in 

 the botanic gardens of Europe as the true Jalap plant ; it is 

 now proved to be an Exogonium, a genus distinguished from 



