A STUDY OF WHEAT. 53 



be seen how great a change is produced in the wall of cellu- 

 lose by boiling. It would be impossible with any one starch 

 grain, or with even a small number, to tell definitely just what 

 treatment, the starch grain has undergone. It is only when you 

 examine a large quantity, and even then you can not tell the 

 extent of the baking or the boiling by its appearance under 

 the microscope. The entire bean, after the' thin skin is re- 

 moved, consists of large cells loaded with starch and glutin. 

 (See figure 12.) The cells are generally hexagonal, thick- 

 walled, and quite large. There are only a few . starch grains 

 contained in each cell, as compared with the way the starch 

 grains of wheat are packed in their cells. Lying close to the 

 walls and filling up all the space between the starch grains, 

 are the fine granules of glutin. 



A microscopical examination of bean flour reveals all of 

 the structures represented in the illustrations, and they are so 

 different from the structures found in wheat, as to be easily 

 identified. Nitric acid forms an important test for the presence 

 of bean flour. Whenever wheat flour with which powdered 

 beans are mixed, is brought in contact with nitric acid and am- 

 monia, it immediately assumes a deep red color. The presence 

 of bean flour, when mixed with wheat flour, may be detected 

 generally by the peculiarly strong odor of beans, and by the 

 darker or yellowish gray color which the wheat flour assumes. 



