58 PHYSIOLOGICAL PROCESSES IN PLANTS 



slight changes in color about the margins of the embryo.) 

 Result ? 



2. Chew some cracker slowly. Is there any change of 

 taste? 



Note. When starch is changed to grape sugar by a sub- 

 stance found in plants or animals, the starch is said to be 

 digested. In plants this may be accomplished by a digestive 

 ferment, or enzyme, called diastase ; in the mouth, by a ferment 

 in saliva (ptyalin). 



Method. Add about 1 gram of diastase powder (commercial) 

 to the same amount of starch and dilute with about 100 times 

 as much water. Set aside in such a place that it will remain at 

 about blood heat. Test for starch at the end of 24 hours. Result? 

 Likewise test for grape sugar. Result? 



Note. A substance is soluble if, when it is put in water, it 

 entirely disappears from view, just as sugar or salt when placed 

 in hot water. 



Conclusions. 1. How do you conclude insoluble starch of 

 plants may be changed into a form which is soluble ? 



2. Of what benefit is it to a plant that its food matter be 

 stored in an insoluble form? 



3. Which sort of food material might more readily circulate 

 about in a plant, starch, or sugar? Explain. 



4. Wliy is it necessary, then, that plants as well as animals 

 digest starchy and other foods ? 



5. What evidently happens when you chew a cracker slowly 

 in the mouth ? 



Questions 



1. Why are beans of value as food for man ? 



2. What other seeds can you name that are used as food 

 for man? 



3. What products come from seeds that are of value as food 

 for man? 



4. In what condition must food material be in order to circu- 

 late in plant or animal bodies? 



