788 



BOTANY AND PHARMACOGNOSY. 



230. RICE STARCH. — This is prepared by the use of chem- 

 icals much the same as in the preparation of corn starch (p. 643). 

 and is either in the form of a white or cream-colored powder or 

 small, irregular masses. The individual grains like those of oat 

 (Fig. 317, E), are polygonal, from 2 to 10 /* in diameter, 

 with a central cleft, and usually united into small aggregates of 

 two or more. The product sold for rice starch is frequently rice 

 flour, and is characterized by the large, oval aggregates of 

 numerous grains, as well as cellular tissue. (See No. 244.) 





Fig. 317. A, starch grains of Iris iiorentina showing peculiar horseshoe-like fissure 

 extending from point of origin of growth; B, irregular starch grains of calumba root; C, 

 peculiar beaked starch grains of ginger rhizome; D, starch grains of bean showing irregular 

 longitudinal fissures; E, compound starch grains of oat. 



231. WHEAT STARCH usually occurs in very hard, some- 

 what elongated and columnar or irregular masses, varying from 

 I to 3 cm. in length. The starch grains are more or less rounded 

 or flattened-circular, and depending upon the surface presented to 

 view under the microscope, appear circular or elliptical in out- 

 line; they vary from 15 to 35 11, in diameter and are without dis- 

 tinct markings except when heated or treated , with dilute acid 

 or alkaline solutions (Fig. 97). When viewed under the micro- 

 polariscope the grains do not show a distinct cross and the play 

 of colors when the selenite plate is used is scarcely discernible. 

 Wheat starch does not agglutinate on mixing with water as 

 wheat flour does (Fig. 95). 



232. OTHER STARCHES.— Among the other commercial 

 starches the following may be mentioned : 



