ORGANIC SUBSTANCES AS PLANT FOOD 209 



was supposed that this was accomplished by diastase. More 

 detailed research has proven, however, that another enzyme, 

 cytase, is at work here, which can be obtained in a comparatively 

 pure state from the germinating seeds of lupine or the stones of the 

 date palm. Like diastase, cytase is formed largely by the embryo. 

 The dissolving of the thickened walls of the 

 endosperm of the date palm stops when the ai-4K~~~~~-^~ 

 embryo is removed. 



Besides these polysaccharide splitting 

 enzymes, there are others at work during 

 germination which hydrolyze the disaccharides 

 and glucosides. Thus, in the conversion of 

 starch into sugar, along with diastase, often 

 maltase is present, which converts maltose 

 into 2 molecules of glucose. Another very 

 widely distributed and much studied enzyme 

 is invertase, which splits cane sugar into FlG -. 91 -~ ; -Longitudinal 



section through the 



glucose and fructose by a process called inver- lower portion of a grain 



sion. It is especially easy to obtain invertase of , whe ^ t (diagrammati- 

 cal). End — endosperm, 

 from yeast, the presence of which leads to i(- a leurone layer, 



hydrolysis of the otherwise not fermentable E " } ; embr y°- Sc scu- 



tellum (after Benecke- 



sucrose. When yeast is triturated with pure j st). 



quartz sand and a small quantity of warm 

 water and filtered, a perfectly transparent filtrate showing a strong 

 invertase action will be obtained. After precipitation by alcohol, 

 a dry preparation of invertase readily soluble in water and pre- 

 serving its action for a rather long time, is secured. 



Of the enzymes which split glucosides, the most important is 

 emulsin or /3-glucosidase, which hydrolyzes all the glucosides of the 

 /3-group. It is usually obtained from seeds of bitter almonds. 

 The enzyme a-glucosidase, closely related to it, acts in the same 

 manner on a-glucosides. It is found along with invertase in the 

 extract from yeast. 



68. General Properties of Enzymes. Methods of Isolation 

 and Purification. — Diastase and cytase belong to the large and 

 very important group of organic catalyzers known as enzymes. 

 Catalyzers are substances which, without themselves taking part in 

 a chemical reaction, speed up the reaction by their presence. 

 They are not found among the end products of a reaction, and they 

 are not used up in the course of the reaction, although their par- 



