128 



PROTECTION OF PLANTS — 1923-24 



2. Four different solid media were chosen, potato-dextrose agar, Czapek's, 

 cornmeal agar and oatmeal agar. Fifteen cc's of the media were poured into 

 each dish and allowed to solidify. 



3. Approximately two weeks before the starting of each series of experi- 

 ments, cultures of each fungus were started, by transferring small bits of 

 medium containing mycelium from a stock culture to the centre of potato- 

 dextrose agar plates. These plates were used as the source of inoculum for the 

 ex'perimental cultures. L-ttle plugs or disks, 5 mm. in diameter and about 2 mm. 

 in thickness were cut by means of a sterile cylindrical tube. Each disk was 

 lifted on the flattened end of a platinum needle and was then inverted and 

 placed centrally upon the surface of a new plate. As the mycelium grew out 

 in every direction from the centre of the plate a rounded mat was formed. 

 The disk remained practically circular as it enlarged, foTming nearly a perfect 

 circle at all stages of enlargement. 



4. Measurements were made at daily intervals for a culture period of 

 ten days. A thin millimeter rule, applied on the bottom of the petri dish 

 outside, was used for measuring the diameter of the growth. Measurements 

 with the millimeter rule were read to within 1 mm. This was thought to 

 be sufficiently precise for the purpose. 



5. All the cultures were grown under exactly the same conditions as to 

 depth of medium, moisture, temperature and light. 



6. In any case where the mycelial disk in the petri did not form an exact 

 circle, the diameter was measured in several places and the average taken. 



The following table and graph show the results: 



Diameter in mm. at the end of 10 days. 



