1919] 



MCGINTY — DIASTASE ACTIVITY OF SOLANUM TUBEROSUM 225 



paste, the rate of activity being determined by the cupric-reduc- 

 ing power of the solution. He used chloroform to inhibit the 

 growth of microorganisms during the time the enzyme was 

 allowed to act, being one of the first to pay attention to this point. 

 The relative amounts of different carbohydrates in plants 

 often bear some relation to enzyme activity ; therefore, the early 

 work of Hungerbiihler ('86), who estimated the carbohydrates 

 at different times in growing potatoes, is of interest here. The 

 following figures give the amounts of reducing sugar, invert 

 sugar, and starch, expressed in percentages of the dry weight, 

 found by him in the tubers at different times: 



June 23 June 30 July 7 



Reducing sugars 6.4 .32 .72 



Invert sugar 



4.50 4.69 



Starch 56.7 61.30 66.30 



Schulze and Seliwanoff ('88) showed the amount of sucrose 

 in immature potatoes to be especially high. Brown and Morris 

 ('90) determined the amounts of diastase present in barley grains 

 at three stages in their development. The results were as follows : 



Relative diastatic 

 activity 



Endosperm half developed 4.4 



Endosperm two-thirds developed 7.8 



Endosperm completely developed 9.7 



These results are in line with the idea that the appearance 

 and increase of the enzyme are related to the formation and 

 nutrition of the embryo. 



The same authors studied the germination of barley grains 

 and found the amount of diastase to increase markedly during 

 the process. The diastatic activity of the barley embryos after 

 different periods of germination was found to be as follows: 



Relative diastatic 

 activity 

 Embryos, dissected from grains which had soaked in 



water for 24 hours Trace only 



Embryos from same barley, but germinated for 3 days on 

 5 per cent gelatin. Diastatic activity of embryos plus 



substrate 1186 



Same, except germinated for 4 days 1634 



Same, except germinated for 6 days 2432 



