66- ELEMENTS OF APPLIED MICROSCOPY. 



h\xt 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 corn 

 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 .004-.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 



f 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- 

 minosae, 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 of 

 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 .02-.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 Arrowroots.^-Arrowroot-starches are exten- 

 sively u.sed as foods for invalids and for certain other 



