64 ELEMENTS OF APPLIED MiCROSCOPY. 
all starches, there is a considerable variation both in shape 
and size; many grains are ellipsoidal, som: three-cor- 
nered, and the smaller ones almost spherical. Near one 
end of the grain the Hilum appears as a well-marked dot, 
surrounded by rather faint concentric ellipses which form 
an important characteristic of potato-starch and are 
known as the oyster-shell markings. Sometimes two or 
more hila appear in a single grain, and often groups of 
two or three grains seem to grow together, as shown in 
Fig. 28 (5). 
6. Wheat-starch.— Wheat-starch makes a very even 
paste and, in spite of its cost, is used in many processes 
where especially fine work is necessary. It is mixed with 
the colors in printing cloth and is utilized in the bleach- 
ing, dyeing, and finishing processes. It is also largely 
used in paper-mills. 
Microscopically, the grains of wheat-starch usually 
appear as somewhat irregular circles, but when tipped up 
on edge their true shape is seen to be lenticular. In size 
they vary from very minute points up to .o4 mm., and it is 
noticeable that the grains are mainly of two sizes, quite 
large and quite small, intermediate grades being rarer 
(Fig. 28 (1)). The hilum can sometimes be made out 
in the largest grains; under the same conditions concen- 
tric circles may indicate the natural layers of the grain, 
though as a rule neither hilum nor markings are apparent. 
7. Corn-starch.—Corn-starch, as we have seen, is in 
America by far the most important of starches, being used 
in the kitchen, the laundry, and the mill for diverse pur- 
poses, as well as for the manufacture of dextrins and 
