TEST FOR GRAPE SUGAR 



59 



our tests that the endosperm is the chief source of food supply. 

 The study of a thin section of the corn grain under the compound 

 microscope shows us that the starch grains in the endosperm are 

 large and regular in size. When the embryo has grown a little, an 

 examination shows that the starch grains near the edge of the coty- 

 ledon are much smaller and quite irregular, having large holes in 

 them. We know that the germinating grain has a much sweeter 

 taste than that which is not growing. This is noticed in sprouting 

 barley or malt. We shall find later that, in order to make use of 

 starchy food, a plant or an animal must in some manner change it 

 to sugar. This change is necessary, because starch will not dis- 

 solve in water, though sugar will ; and in fluid form substances can 

 pass from cell to cell in the plant and thus go where they are needed. 

 A Test for Grape Sugar. — Place in a test tube the substance to 

 be tested and heat it in a little water so as to dissolve the sugar. 



liliii 



+ 



V 



^^ 



HEAT 



Colors seen in test for grape sugar. 



A, a dry corn grain; B, a 

 germinated corn grain, tested 

 for grape sugar. 



Add to the fluid twice its bulk of Fehling's solution. ^ Heat the 

 mixture, which should now have a blue color, in the test tube. If 

 grape sugar ^ is present in considerable quantity, the contents of the 

 tube will turn first a greenish, then a yellow, and finally a brick- 

 red color. Smaller amounts will show kss decided red. No other 



^ Directions for making Fehling's solution, and Benedict's solution (page 60), will 

 be found in Hunter's Laboratory Problems iii Civic Biology. 



2 Grape sugar, or glucose, is a simple kind of sugar found in many plants. 



