20 BULLETIN 183, U. S. DEPARTMENT OF AGRICULTUEE. 



as corn grits or brewers' rice, are used in conjunction with malt, the 

 same type of malt is popular, although an extreme development of 

 diastase is not here demanded, because the additional amount of 

 starch to be converted is less. 



The explanation of the greater enzymatic power of small-berried 

 barleys seems simple. The diastase-secreting surface is confined to 

 the epithelial layer. The proportion of epithelial surface to volume 

 of endosperm should also represent the ratio of diastase to starch. 

 For the purpose of illustration, the shape of the barley grain may be 

 considered as a sphere, while the curve of the scutellum may be 

 taken to represent that of a second sphere partly included in the first. 

 If the size of the grain is made greater, its volume is increased much 

 more rapidly than the area of the surfaces of the spheres, according 

 to well-known laws of geometry. That is to say, for any increase in 

 the size of the grain the increase in the area of the surface of the 

 scutellum is much less proportionately than the increase in the vol- 

 ume of either the embryo or the endosperm; and, conversely, as a 

 grain decreases in size the epithelial surface decreases much less pro- 

 portionately than the bulk of its endosperm. It is therefore but 

 natural that the diastase production in a small grain should be rela- 

 tively greater than in a large one and often greatly in excess of the 

 needs for conversion. 



■ The relation of diastatic power to nitrogen content is a slightly 

 more complex problem. In general, barleys high in nitrogen are 

 also high in enzymatic power. The case varies somewhat with con- 

 ditions. In the smaU-berried barley the same facts apply as in the 

 ratio of scutellar surface to endosperm. The aleurone layer is one of 

 the great sources of nitrogen in the barley grain. This layer is 

 almost invariably three cells deep. If the grain be very small, the 

 two or three layers of cells completely encircHng the starch endosperm 

 form a very considerable part of the grain. Since they are high in 

 nitrogen, this element tends to represent a higher and higher percent- 

 age of the total as the diameter of the grain is progressively reduced. 

 In a very small grain the percentage of nitrogen is therefore likely 

 to be high, even though the starch endosperm be ever so mealy, the 

 decidmg factor bemg, of course, the great proportion of the aleurone 

 layer. 



There is, however, among the 2-rowed barleys a different situation, 

 in that climate and culture assume a greater importance. Barley- 

 growing areas are often conspicuous for their production of high- 

 nitrogen barleys. Indeed, the crops of any section vary in this re- 

 spect from year to year. It is ahnost invariably the case that these 

 high-nitrogen crops are also high in diastatic power, often possessing 

 an enzymatic potency almost equal to that of the smaU-berried sorts. 

 In these cases, also, the explanation is found in the ratio of the 



