Plants in Relation to Man 519 



by the plant during its day's work, is made soluble by a par- 

 ticular kind of digestive ferment or enzyme known as diastase. 

 Diastase dissolves the starch grains produced in the leaves, 

 converting them into sugar, which being soluble is taken into 

 the circulation and distributed among the various centers of 

 growth. This enzyme, generally inactive or even absent in 

 the bright sunlight, becomes especially abundant in the dark, 

 so that by the return of the daylight the starch has been di- 

 gested and removed from the leaves. Thus the leaves are 

 made ready for another day's labor in producing food. 



Diastase is not confined merely to the leaves, but is found 

 in new stems, buds, and other actively growing parts of the 

 plant. Here it does the same work of changing starch into 

 sugar. It is found also in potato tubers and especially in the 

 neighborhood of " eyes " where growth occurs. It is plentiful 

 in the seeds of cereals and grasses. One of the best examples 

 of the working of diastase is furnished in grains of barley. One 

 finds by tasting barley grains that the endosperm is not sweet. 

 Barley grains soaked in water have the same starchy nature. 

 But taste the endosperm of grains which have just begun to 

 sprout (sprout them between sheets of damp blotting paper) ; 

 this is found to be sweet, in fact is a kind of sugar which has 

 been produced by diastase acting upon the starch of the grain. 



Experiment. The conversion of starch into sugar very much in 

 the manner of its digestion in the plant may be illustrated by a simple 

 experiment. Make a thin starch paste in a beaker. Add five drops 

 of hydrochloric acid and boil slowly for twenty minutes. With a 

 glass rod put a drop of it on blue litmus paper. If the solution is 

 acid, it will turn the paper red. Dissolve a level teaspoonful of bicar- 

 bonate of soda in about ten times its volume of water. Add the soda 

 solution very gradually to the starch paste, testing this from time to 

 time with litmus paper until it fails to give the acid reaction. The 

 acid of the solution should be just neutralized. The solution is found 

 to be sweet to the taste, due to a kind of sugar called glucose, which is 

 soluble in water and similar to the sugar made by diastase acting upon 

 starch in the plant. 



