FOODS AND DRUGS AND THEIR ADULTERANTS. 75 
mal layers are difficult to make out clearly. Within 
them lies a characteristic tissue known as the columnar 
layer made up of prismatic cells which, as seen under the 
microscope, are small and polygonal with heavy walls 
and small central lumens, giving the whole a dotted ap- 
pearance. In white mustard (B. alba) this tissue is yel- 
lowish, while in black mustard (B. nigra) it is dark 
brown, determining in each case the general color of the 
Fic. 30.—MIcroscoPic STRUCTURE OF Mustarp. (After Schimper.) 
240 diameters. 
seed (6, Fig. 30). Finally, the interior is a tissue of 
medium-sized, fairly thick-walled cells, packed with a 
fine, gray-green, granular material containing . oil-drops 
(a, Fig. 30). 
6. Adulterants of Mustard.—In a good table-mustard 
the amounts of epidermal and columnar tissue present 
are very small, since the hulls are largely sifted out; the 
