30 FLOURS. 



(22) Barley Flour. 



In many respects barley resembles wheat and rye in its ana- 

 tomical structure. One of the principal differences is to be found 

 in the hairs which have a larger lumen than those of either wheat 

 or rye. The walls of the epidermal cells of the pericarp are not 

 pitted, nor are they so thick as those of the two latter grains. The 

 aleurone layer invariably consists of two or three rows of cells, 

 whereas in the wheat and rye there is only one row. 



The grains of barley starch are smaller than those of wheat, and 

 much smaller than those of rye. They are less regular in shape, 

 and frequently reniform, but these characters are difficult even for 

 an expert to determine, and the detection of barley flour when 

 mixed with wheat or rye flour is very difficult. There is, however, 

 one peculiarity that may facilitate the identification of barley flour. 

 The barley grain is enclosed between two palese, and these adhere 

 so firmly to the pericarp of the fruit that it becomes very difficult 

 to effect their complete removal, especially from the groove on the 

 ventral surface of the grain. The result is that barley flour often 

 contains traces of the debris of the palese, and these are easily 

 identified by the very remarkable sinuous walls of the outer epi- 

 dermal cells, and by the little hairs on the inner epidermis. The 

 double or triple layer of aleurone cells should also be searched for. 



The diagnostic characters of barley flour are : 



(a) The epidermal cells of the palece, with thickened, sinuous walls. 



(b) The hairs on the inner epidermis of palea. 



(c) The thin-walled and not pitted epidermal cells of pericarp. 



(d) The aleurone layer of two or three rows of cells. 



(e) The starch grains, which are rather smaller than those of 

 wheat, and often more irregular in shape. 



