CRUDE DRUGS. 



651 



to Southeastern Europe and Western Asia (p. 294). Some of 

 the walls of the pith and medullary rays are transformed into 

 mucilage (Fig. 274), which exudes spontaneously, but is obtained 

 in commercial quantities by making incisions in the bark, the gum 



ms 



mst 



Fig. 274. Cross section through pith (m) and the inner portion of the wood (lb) 

 of Astragalus gummifer showing stages in the modification of the cell-walls in the formation 

 of gum tragacanth (0,1,2,3, 4). Some of the tracheae (c) contain globular masses of gum. 

 After Tschirch. 



being collected after it dries. The principal points of export are 

 Smyrna and various ports along the Persian Gulf ; that obtained 

 from the latter is known as Persian or Syrian Tragacanth and 

 is preferred. 



