JALAP 553 



extensively cultivated in tropical countries on account of the edible 

 tuberous roots. The roots contain from 3 to 10 per cent of sugar 

 and 9 to 15 per cent of starch, which occurs in larger proportion in 

 plants grown in sub-tropical countries. The starch is a commer- 

 cial product and is known as sweet-potato starch or BRAZILIAN 

 ARROW-ROOT. The starch grains are either single or 2- to 6-com- 

 pound, the individual grains from 0.005 to 0.055 mm. in diameter, 

 mostly plano-convex, resembling cassava starch grains, also spheroi- 

 dal and polyhedral forms occur. 



The plants of the Convolvulacese possess a number of interesting 

 anatomical characteristics. Secretory cells, having suberized walls, 

 occur either as isolated cells or arranged in long vertical rows. They 

 are either oblong or flask-shaped and contain a milky content, which 

 is either colorless or yellowish-brown and soluble in alcohol. Laticif- 

 erous vessels, consisting of a non-suberized, thick-walled, tubular, 

 latex-receptacles, have been found only in Dichondra. The fibro- 

 vascular bundles with few exceptions are of the bi-collateral type. 

 The tracheae possess simple pores. The wood fibers are marked 

 by bordered pores and the medullary rays are narrow. Calcium 

 oxalate is secreted in the form of small needles, small rods, solitary 

 crystals and rosette aggregates, the latter sometimes occurring in the 

 idioblasts of the leaves. The non-glandular hairs usually consist of 



2 cells, the lower or stalk having a suberized wall. The glandular 

 hairs usually have a unicellular stalk and a multicellular head. In 

 the leaves, the subsidiary cells are placed parallel to the pores of the 

 stomata. A very complicated anomalous structure is seen in the 

 fleshy roots of jalap and scammony. 



JALAPA. Jalap. The tuberous root or tubercle of Exogonium 

 Purga (Fam. Convolvulacese), a perennial twining herb, native of the 

 eastern slopes of the Mexican Andes, and cultivated in Jamaica and 

 India. The roots are collected in the fall and dried by artificial means, 

 the larger ones being first cut into longitudinal pieces. Mexico fur- 

 nishes the principal part of the commercial supply, which is exported 

 from Vera Cruz. 



Description. Fusiform, irregularly ovoid or pyriform, upper 

 end more or less rounded, lower end obtuse or slightly acuminate; 



3 to 8 cm. in length, 1 to 5 cm. in diameter; externally dark brown, 

 deeply and irregularly furrowed longitudinally, otherwise nearly 

 smooth or wrinkled, with numerous lenticels 2 to 4 mm. in length 

 and few circular rootlet-scars; fracture horny and resinous; Internally 

 dark brown and marked by more or less distinct, secondary, concen- 

 tric cambium zones; odor fruity; taste starchy and slightly acrid. 



