72 



SEEDS AND SEEDLINGS 



in the mouth for a httle time, it will begin to taste sweet, and if the 

 chewed cracker, which we know contains starch, is tested with 

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

 to grape sugar. Here again a process of digestion has taken 

 place. In both the corn and in the mouth, the change is brought 

 about by the action of peculiar substances known as digestive 

 ferments, or enzymes, and the result is that substances which 

 before digestion would not dissolve in water now will dissolve. 



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

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

 is called diastase. It may be separated from the cotyledon and 

 used in the form of a powder. 



To a little starch in half a cup of water we add a very little (1 

 gram) of diastase and put the vessel containing the mixture in a 

 warm place, where the temperature will remain nearly constant at 

 about 98° Fahrenheit. On testing part of the contents at the end 



of half an hour, and the 

 remainder the next morn- 

 ing, for starch and for 

 grape sugar, we find from 

 the latter test that the 

 starch has been almost 

 completely changed to 

 grape sugar. Starch and 

 warm water under similar 

 conditions will not react 

 to the test for grape sugar. 



Germinating corn grains, 

 if deprived of their endos- 

 perm, soon die. But if the 

 endosperm is removed and a 

 little corn starch paste be 

 stuck to the little plant in 

 place of the endosperm, the 



development of the embryo will be but little affected (see Figure). 



Evidently the enzyme formed in the cotyledon has the power to digest 



the starch paste, and the cotyledon transfers the digested food to the 



growing parts of the embryo. 



The use of the endosperm to the corn : A, seed- 

 lings without endosperm ; B, seedlings with 

 starch in place of endosperm ; normal seed- 

 hngs at the center. 



