FACTORS INFLUENCING DIASTASE FORMATION 223 



stituted because it was found impossible to distinguish between 

 the moisture held in the outer covering of the kernel and that 

 of the kernel proper. Brown (1909) experienced a similar diffi- 

 culty. He says, 



It should be pointed out that the determinations on which the 

 curves arc based are affected by an unavoidable error due to the man- 

 ner in which the values are arrived at. Some allowance should be made 

 for the amount of water absorbed by the outer covering of the seeds. 

 It is not possible to evaluate this amount very closely; apparently, 

 however, it may be taken as equal to about 8% of the original weight 

 of the dry seeds. 



An error of 8% in moisture content is far too large, since the 

 respiration, as we have already seen, is markedly affected by 

 far smaller moisture variations. We shall see later that this is 

 also true of diastase actiyity in the seed. 



Moisture control 



Two methods, both successful, were used to bring the barley 

 grains to the desired moisture content. The first, which might 

 be termed the immersion method, was used when a relatively 

 high water content was desired and the period of experimenta- 

 tion did not exceed 12 hours. The second, which might be 

 termed the vapor tension method, was used in the greater number 

 of experiments. It permits of a far more delicate control of 

 moisture content and the desired content, once reached, can be 

 maintained, under proper conditions, almost indefinitely. It 

 cannot be used where a moisture content sufficiently high for 

 germination, or nearly so, is desired. 



The immersion method 



Brown (1909) first called attention to the fact that the mem- 

 branes covering the barley grain are semi-permeable in nature. 

 In consequence of this and the strong affinity for water of the 

 grain itself, it is possible by varying the density of the solution 

 to furnish the grain a definite quantity of water. Schroeder 



