MYCORHIZAS 



245 



of bread in water for half a day, then place it in a dish under a 

 bell-jar in a room at ordinary temperatures. A number of 

 species of whitish moulds will be produced at first, followed in a 

 few days by masses of bluish Penicillium. Both kinds live on the 

 organic material contained in the bread, but the determination of 

 the food constituents may be made by the following cultures. 

 Make a nutrient solution as follows : 



100 cc. distilled water. 



.05 gram ammonium phosphate. 



.05 gram acid potassium phosphate. 



.03 gram magnesium sulphate. 



.01 gram calcium chloride. 



A drop or two of iron sulphate. 



Divide the solution into four parts and place in Petri dishes. 

 Leave one dish unchanged, to a second add .02 g. grape sugar, to 

 the third add .02 cc. oxalic acid, and to 

 the fourth add .02 cc. citric acid. Acidu- 

 late the first and second dishes with a 

 drop or two of dilute sulphuric acid. 

 Take a small mass of spores of Penicil- 

 lium from the bread culture and place 



FIG. 121. Portions of root of Tsuga Canadensis, with club-shaped mycorhizas. 

 After Harlow. 



FIG. 122. Longitudinal section of mycorhizal root of Tsuga Canadensis. The 

 outer layers are inhabited by a fungus. After Harlow. 



in each dish. Set the dishes in a dark room at a temperature 

 of 16-20 C. and note condition a week later. This should 

 demonstrate which of the added organic substances will serve as 



