i6 IVHAT THE PLANT IS MADE OF [chap. 



which can convert starch into sugar. This substance in 

 the extract of the germinated barley belongs to the 

 class of bodies known as enzymes, or soluble ferments ; it 

 is called diastase, and it is secreted by the active growing 

 embryo of the barley, its function being to convert the 

 stored-up starch of the endosperm into soluble sugar 

 which can travel to the growing points of the plant. 

 There are many kinds of enzymes secreted by both 

 animals and plants ; they are mostly soluble in water ; 

 they all work most rapidly at a temperature of 50° to 

 60° C. (122° to 140° R), and are destroyed at or below the 

 temperature of boiling water. By very similar experi- 

 ments we can show that the germinating seed also 

 contains a protease, i.e. an enzyme attacking the 

 insoluble proteins and converting them into soluble 

 amino and amido bodies. Pepsin and papain are 

 commercial proteases, extracted one from an animal the 

 other from a plant, and it is easy to show that they will 

 dissolve insoluble proteins like fragments of boiled 

 white of egg or gluten. Similarly, the embryos of 

 germinating seeds of mustard or flax secrete a lipase, 

 or fat-splitting enzyme, capable of reducing fat to soluble 

 substances which can traverse the plant and be utilised 

 at the growing points. 



The germinated barley from which we have just'been 

 extracting diastase is nothing but incipient malt; the 

 process of malting consists in steeping good well-ripened 

 barley for forty-eight hours, and then spreading it in a 

 layer 4 to 12 inches thick on floors to germinate. After 

 ten or eleven days, when the rootlets are almost twice as 

 long as the grain, the barley is slowly and carefully 

 dried at a temperature not exceeding 180° F. Finally 

 it is screened to knock off the rootlets, and put into 

 store. The germination process develops a quantity of 

 diast£ise which accumulates in the embryo and is not 



