60 PLANT GROWTH AND NUTRITION 



food substance than grape sugar and certain other sugars will 

 give this reaction.^ If Benedict's test is used, a colored precipitate 

 will appear in the test tube after boiling, if grape sugar is present. 

 Starch changed to Grape Sugar in the Corn. — That starch is 

 changed to grape sugar in the germinating corn grain can easily 



be shown. First, cut length- 

 wise through the embryos of half 

 a dozen grains of corn and test 

 with Fehling's solution to show 

 that no grape sugar is present. 

 Then test in the same way some 

 lAfheBf Oaf Besn Corn Pes ^^^:^^^ ^j^^^ have just begun to 



Starch grains, magnified. • , i ^u •^^ ' 



germmate, and they will give a 

 reaction showing the presence of sugar along the edge of the 

 cotyledon and between it and the endosperm. 



Digestion. — This change of starch to grape sugar in the corn 

 is due to a process called digestion. If you chew for a little time 

 a bit of unsweetened cracker — which we know contains starch — 

 it will begin to taste sweet, and if the chewed cracker is tested with 

 Fehling's solution, some of the starch will be found to have changed 

 to grape sugar. Here, again, the process of digestion has taken 

 place. Both in the corn and in the mouth, this change is brought 

 about by the action of chemical substances known as digestive 

 ferments, or enzymes (en'zimz). Such substances have the power 

 under certain conditions to change insoluble foods — solids — into 

 soluble substances. The result is that foods which before diges- 

 tion would not dissolve in water will dissolve after being digested. 



The Action of Diastase on Starch. — The enzyme found in the 

 cotyledon of the corn, which changes starch to grape sugar, is 

 called diastase (dfd-stas) . It may be separated from the cotyledon 

 and is prepared by chemists for use in the form of a powder. 



To a little starch in half a cup of water add a very little diastase 

 (1 gram) and put the vessel containing the mixture in a warm place, 

 where the temperature will remain nearly constant at about 98° 

 Fahrenheit. Testing part of the contents at the end of half an 

 hour, for starch and for grape sugar, we find both of them present. 

 If the rest of the mixture is tested the next morning, it will be 



1 Ordinary cane sugar or beet sugar will not give this reaction. 



