POWDERED DRUGS AND FOODS. 789 



a. Consisting of Single Grains: Yam starch (from several 

 species of Dioscorea) occurs in narrow, ellipsoidal grains, 30 to 50 

 IX long, with distinct lamellae and point of origin of growth at nar- 

 row end. Canna starch (tons les mots arrowroot), derived from 

 several species of Canna, occurs in broadly elliptical or ovate grains 

 varying from 50 to 125 ;«, in diameter and with distinct lamellae 

 and circular point of origin of growth. Bean starch consists of 

 ellipsoidal or reniform grains, which vary from 25 to 50 ju in 

 length and have a distinct, branching, elongated cleft in the middle. 

 PEA-starch grains resemble those of bean starch, but the grains 

 are smaller and more or less irregular on the surface (Figs. 95; 



317,^). 



b. Consisting of 2- to 3-coMPOUND grains : Cassava or tapi- 

 oca starch is obtained from the Sweet and Bitter Cassava (p. 

 318), and occurs in somewhat plano-convex or bell-shaped, 2- to 

 3-, or even 4- to 8-compound grains, which vary from 6 to 30 /* 

 in diameter and have a distinct central, circular, or radiating cleft. 

 Sweet potato starch resembles Cassava starch, but some of the 

 grains are larger. 



h. ALTERED AND UNALTERED STARCH GRAINS PRESENT. 



233. DEXTRIN. — Sticky mass with water, consisting chiefly 

 of altered starch grains, but usually sufficient unaltered grains 

 are present to determine the source of the dextrin. 



234. SAGO starch is obtained from Cycas revoluta and other 

 cycads as well as a number of palms (p. 233). It occurs iiT 

 commerce in small, horny granules, which are slowly affected! 

 by cold water, when there separates the characteristic elliptical! 

 or truncate-elliptical starch grains. The latter vary from 15 

 to 50 fi, long and have a large central area surrounded by rather 

 narrow, distinct, altered lamellae. 



235. SAGO (IMITATION).— Breaks down quickly in water 

 and shows characteristic corn starch grains. 



C. PLANT TISSUES IN ADDITION TO STARCH GRAINS. 



The former remain upon treatment with hot glycerin. 



