58 PLANT PHYSIOLOGY 



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. 15) and the aleurone layer 

 surrounding the endosperm. Thence it diffuses into the tissue 

 of the endosperm, causing decomposition of the starch stored 

 there. It is interesting to note that the conversion of starch 

 -._ £nd into sugar in the endosperm proceeds to comple- 



tion only if the starch remains in close contact 

 with the scutellum and the young sprout adjacent 

 to it, which continually absorbs and utilizes the 

 sugar formed during the hydrolysis of starch. If 

 these parts are removed, the process of trans- 

 formation 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 

 Fig. 15.— Lon- starch, the cell walls of the endosperm also are 



gitudinai section jjggQiyg^i ^t germination. Formerly, it was sup- 

 through the lower ^ t i i i 



portion of a grain poscd that this was accomplished by diastase, 



of wheat (diagram- y^^^^ detailed research has proved, however, that 



matical). ii/ict — , ^ u • u 



endosperm, Ai— another enzyme, cytase, is at work here, which 

 aleurone layer ,^m ^^ obtained in a comparatively pure state 



— embryo, be — i c i • i_ j 



scutellum {after from the germinating seeds of lupine or the seeds 

 Benecke-Jost). ^^ ^^^ ^^^^ palm. Like diastasc, cytase is formed 



largely by the embryo. The dissolving of the thickened walls of 

 the endosperm of the date palm stops when the embryo is 



removed. 



Besides these polysaccharide-splitting enzymes, there are 

 others at work during germination that hydrolyze the disac- 

 charides and glucosides. Thus, in the conversion of starch into 

 sugar, along with diastase, often maltase is present, which 

 changes maltose into 2 molecules of glucose. Another very 

 widely distributed and much studied enzyme is invertase, which 

 sphts cane sugar into glucose and fructose by a process called 

 ''inversion." It is especially easy to obtain invertase from 

 yeast, the presence of which leads to hydrolysis of sucrose which 

 otherwise is not fermentable. When yeast is triturated with 

 pure quartz sand and a small quantity of warm water and 



