POTATO MEDIA 



177 



into boiling water to destroy the oxidizing enzyme on the 

 surface which would otherwise cause a darkening of the 

 potato. (The darkening may also be prevented by keeping 

 the freshly cut potatoes covered with clean water until 



Fig. 112.— Petri dish wath the lid partly raised. 



Fig. 113.— a potato plate. X h 



ready to sterilize.) A bit of cotton one-fourth to one-half 

 inch in depth is put into each of the test-tubes to retain 

 moisture and a piece of potato dropped in, circular base 

 down. The tubes are then plugged with cotton and steril- 

 12 



