PLANT GROWTH AND NUTRITION 



69 



soluble substances —liquids. 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 con- 

 tents at the end of half an hour, and the 

 remainder the next morning, for starch and 

 for grape sugar, we find from the morning 

 test that the starch has been almost com- 

 pletely changed to grape sugar. Starch 

 and warm water alone under similar con- 

 ditions will not react to the test for grape 

 sugar. 



Digestion has the Same Purpose in Plants 

 and Animals. — In our own bodies we 

 know that solid foods taken into the mouth are broken up by the 

 teeth and moistened by saliva. If we could follow that food, we 

 would find that eventually it became part of the blood. It was 

 -made soluble by digestion, and in a liquid form was able to reach 

 the blood. Once a part of the body, the food is used either to 

 release energy or to build up the body. 



Summary. — We have seen : 



1. That seeds, in order to grow, must possess a food supply 

 either in or around their bodies. 



2. That this food supply must be oxidized before energy is 

 released. 



3. That in cases where the food is not stored at the point 

 where it is to be oxidized the food must be digested so that it 

 may be transported from one part to another in the same plant. 



A germinating corn grain. 

 C, cotyledon; H, grow- 

 ing root (hypocotyl); P, 

 growing stem (plumule) ; 

 S, endosperm; d.s., di- 

 gested starch; p.r., pri- 

 mary root; s.r., second- 

 ary root; r.h., root hairs. 



