66 ELEMENTS OF APPLIED MICROSCOPY. 
but approximately isodiametric, it shows very black edges 
in air- and water-mounts. Concentric layers are absent; 
but the hilum is sharply marked, showing in water- 
mount the form of a cross with cracks radiating out 
toward the periphery of the grain. In denser media this 
effect disappears and the hilum is seen to be round (Fig. 
28 (2)). 
8. Rice-starch.—Rice-starch resembles that of com 
in a general way, being polyhedral in shape with distinct 
facets and angles. It is very much smaller, however, 
having an average diameter of about .oo4-.008 mm., and 
the grains are rather regular in size. Another character- 
istic is found in the fact that the grains commonly occur 
aggregated in masses. As a rule no hilum can be seen 
(Fig. 28 (3)). This starch is used to some extent as an 
‘adulterant, and as a constituent of various powders. 
9. The Starches of the Pea and Bean.—The pea and 
bean, as well as certain other plants of the order Legu- 
minosz, have starches of a very characteristic type; and 
though not of special importance in themselves, an ac- 
quaintance with their appearance is an important aid in 
the detection of adulteration with the ground-seeds ®f 
these species. Bean-starch, which may be taken as an 
example of this group, has grains of an elliptical or kid- 
ney shape with a size of .o2-.06 mm. The hilum has 
the form of a slit running the long way of the grain, 
while distinct concentric layers may be made. out in a 
good light (Fig. 28 (6)). 
10. The Arrowrocts.—Arrowroot-starches are exten- 
sively used as foods for invalids and for certain other 
