64 ELEMENTS OF APPLIED MICROSCOPY. 



all starches, there is a considerable variation both in shape 

 and size; many grains are ellipsoidal, soni, three-cor- 

 nered, and the smaller ones almost spherical. Near one 

 end of the grain the liilum 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 .04 mm., and it is 

 noticeable that the grains are mainly of two sizes, quite 

 large and quite small, intermediate grades being rarer 

 (Fig. 28 (i)). 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 



