CONVOLVULUS TRIBE. SCAMMONY ; JALAP ; DODDER. 477 



species of temperate climates, which seem as if they had not time 

 to elaborate them, than in those which increase from year to year, 

 and form woody roots and stems. 



652. It is among these last, that the peculiar characters of 

 the order chiefly manifest themselves. They form an acrid resi- 

 nous matter, possessing active purgative properties. This is 

 especially abundant in the roots and rhizomas ; and it is obtained 

 from several species for medicinal purposes. The resinous ex- 

 tract known as Scammony^ is the milky juice, obtained from a 

 species that grows in the countries bordering on the Levant, and 

 hardened by exposure to the air. The high price of this drug 

 partly depends upon the heavy duty to which it is subjected ; 

 and it is one extremely liable to adulteration. The drug known 

 as Jalap is the powdered root of an American species, from which 

 also a resinous extract might be obtained ; but *the active prin- 

 ciple exists so largely in the roots, that there' is no necessity for 

 thus concentrating it. When administered in proper doses, it is 

 a safe as well as active medicine ; it is also a very cheap one ; 

 and a very large quantity of it is accordingly consumed in this 

 country, between 2 and 300,000 Ibs. being annually imported, 

 chiefly from Yera Cruz. The common Bindweed of this coun- 

 try has similar properties in a less degree. There are some 

 species of Convolvulus, however, which form a large fleshy root; 

 and the resin contained in this exists in such small proportion to 

 the starch, that it forms a harmless and nutritious article of food. 

 These roots are known in tropical countries (in some of which 

 they are much employed) under the name of Sweet Potatoes. 

 The leaves and young shoots of these may also be eaten as 

 pot-herbs. 



653. This order includes a curious parasitic group, that of 

 the various species of Cuscuta or Dodder, whose general habits 

 have been already described (. 344). The Dodder may be 

 frequently seen on the stems of Heath, Furze, or Nettles, in the 

 form of a cluster of stout reddish cords, which are so entwined 

 together, that they might be almost taken for a knot of young 

 snakes. The only vestiges of leaves consist of a few stunted 

 scales ; and it ie curious that the cotyledons also are nearly 



