208 TEXTBOOK OF PLANT PHYSIOLOGY 



the whole process usually stops at the maltose stage. Diastase 

 reduces step by step the colloidal aggregate which we call starch, 

 in other words, it increases the degree of its dispersion. It pro- 

 duces first the intermediate products of the breaking-up process, 

 the dextrines (having properties very close to, if not identical with, 

 glycogen), and then maltose, where its action ceases. It is not 

 able to split maltose into glucose. 



Besides its gradual action, diastase differs from inorganic 

 catalyzers also by its specificity. It can act only upon starch, but 

 produces no effect on the reserve celluloses, which are hydrolyzed 

 by acids with no greater difficulty than is starch. Likewise it has 

 no effect either on inulin or cane sugar. 



Only a very small quantity of diastase is present in dormant 

 seeds; hence, during the early stages of germination, the decompo- 

 sition of starch proceeds very slowly. At the time of swelling, 

 however, the quantity of diastase in the seed increases noticeably, 

 and during the first few days of germination it shows a marked 

 increase. At the end of the first week of germination the amount 

 of diastase is usually three to four times as great as it was at the 

 completion of swelling. This increase of diastase with the progress 

 of germination takes place only in the presence of a sufficient supply 

 of oxygen and is most closely connected with the very active respir- 

 ation shown by germinating seeds. If the seeds are deprived of 

 oxygen, the accumulation of diastase ceases at once. 



In the grain of cereals, such as wheat and corn, the centers of 

 formation of diastase are predominantly the embryo of the seed, 

 especially its scutellum (Fig. 91), and the aleurone layer surround- 

 ing the endosperm. Whence it diffuses into the tissue of the endo- 

 sperm, causing decomposition of the starch stored in it. The 

 endospermal tissue proper appears to be lifeless. It is interesting 

 to note that the conversion of starch into sugar in the endosperm 

 proceeds to completion only if the starch remains in close contact 

 with the scutellum and the young sprout adjacent to it, which con- 

 tinually absorbs and utilizes the sugar formed during the hydrolysis 

 of starch. If these parts are withdrawn, the process of the 

 transformation of starch in the endosperm stops quickly as a 

 result of the accumulation of the soluble end products of the 

 reaction. 



Simultaneously with the decomposition of starch, the cell walls 

 of the endosperm also are dissolved at germination. Formerly it 



