A STUDY OF WHEAT. 



57 



are more opaque and thicker than the others. The small 

 grains are quite numerous and very small ; they are smaller 

 than the corresponding grains of wheat, while the large grains 

 are very much larger. A strongly marked cross is seen with the 

 polarized light in the large grains of rye starch. 



Oat was formerly much used as food for man, especially in 

 cool climates, where it is cultivated with the best success. 

 Its native country is not certainly known, though probably North- 

 ern Europe or Asia. There are several distinct species of oats, 

 the one generally cultivated in this country is avena sativa. Oat 



Fig. j. Oat Starch. X 475. (Drawn with the camera lucida.) 



flour does not form a dough or paste like wheat flour, so it 

 can never be used as a substitute, although it is frequently 

 mixed with wheat and sold under the name of wheat flour. 

 Oat flour, however, contains a large amount of nitrogenous mat- 

 ter. The grains or kernels of oat are usually found in market 

 inclosed in their husks. The first fruit coat of oat is com- 



