168 EXPERIMENTS WITH PLANTS 



fact that the starch is changed to dextrin, a substance 

 familiar to us in the crust of bread, where it is formed 

 by the action of the heat on the moist starch of the 

 flour. The characteristic color and taste of the crust 

 are due to the dextrin, also its stickiness when moist- 

 ened with water (dextrin is used commercially as 

 mucilage) . After the acid solution has boiled for a 

 sufficient time the dextrin is all changed to grape- 

 sugar, as will appear upon testing. 



In seeds which contain starch we may expect to 

 find ferments which have the power of hydrolyzing 

 starch and converting it into soluble form; i. e., into 

 sugar. The most favorable seed for examination is 

 Barley, but any Grain will serve the purpose excel- 

 lently. Grind some of the dry grain in a mortar with 

 water, filter, and to the filtered liquid add twice its 

 volume of Fehling's solution and boil. Allow it to 

 stand, and note the amount of precipitate. Do the 

 same with some Barley which has so far germinated 

 that the caulicle is about a quarter of an inch long. 

 What difference in the amount of precipitate ? Has the 

 amount of grape-sugar increased? Grind up some 

 more dry grain in water, filter, and add to the filtered 

 liquid a little starch. After twenty-four hours, test for 

 grape-sugar with Fehling's solution. 



The first step in the process of brewing is to allow 

 Barley to germinate until the starch is mostly changed 

 to sugar; the grain is then killed by heat and a watery 



