128 WHY DO SEEDS GERMINATE? 



PROBLEM VII. HOW DOES THE CORN GRAIN MAKE USE 

 OF STORED FOOD? 



Demonstration 9. How is the endosperm used ? 



Remove the endosperm from some corn grains that have just started 

 to sprout. Place them in moist sawdust side by side with some normal 

 sprouted grains. Give each lot of seedlings the same conditions of 

 water, light, and air. 



Watch them carefully for at least two weeks. What differences do 

 you observe in the rates of growth in the two lots of seedlings ? 



Conclusion. What is the relation of the endosperm to growth? 



Changes in the food supply of a seed during germination. We 



have learned that the chief source of the food supply of the corn 

 grain is the endosperm which contains starch and also some pro- 

 tein in its outer parts. These foods are in an insoluble form. In 

 order that the growing embryo may make use of the stored nutri- 

 ents they must be changed into a soluble form so that they may 

 be carried out of the endosperm through the cotyledon to the 

 growing parts of the embryo. Starch can easily be changed by 

 the process of digestion into grape sugar or glucose 1 which is 

 soluble. We know that the germinating corn grain has a sweeter 

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

 sprouting barley or malt. The germinating grain contains grape 

 sugar which has been formed from the starch. This, with protein 

 which has also been digested in the endosperm, passes from cell 

 to cell and thus reaches the growing part of the embryo. 



This process of chemical change- or digestion cannot take place 

 in dry seeds. Water must be absorbed by the seed, first, in order 

 to allow digestion to take place and, second, to allow the soluble 

 material to dissolve and pass through the cells. This digestion 

 cannot take place without a moderate degree of warmth. For 

 this reason moisture and warmth are necessary for germination. 



Test for grape sugar. Just after the test for starch was worked 

 out, a chemist by the name of Fehling prepared a solution which 

 is named in honor of him and which is used as a test for glucose. 

 An American chemist, Dr. Benedict, modified this solution and we 

 can now use either the Fehling or the Benedict solution as a test 

 for glucose. 



1 Grape sugar, or glucose, is a simple kind of sugar found in many plants and is 

 the form in which digested starch is passed on to the plant cells. 



