FOODS AND DRUGS AND THEIR ADULTERANTS. 75 



mal layers are difficult to make out clearly. Within 

 them lies a characteristic tissue known as the coluijinar 

 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 



Fig. 30. — ^Microscopic Structure of Mustard. (After Schimper.) 

 240 diameters. 



seed (b, 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 



