ROSE CANKER AND ITS CONTROL. 



31 



ice boxes and constant temperature rooms, wherever a constant temperature could 

 be maintained for a week at a time. A new line was drawn at the end of every 

 forty-eight hours. 



The results of this test are tabulated in Table III. An examination 

 of this table shows that the optimum temperature for growth is 26 to 

 27° C, the minimum is just above 8.5°, and the maximum between 30° 

 and 32°. At the optimum, the mycelium grows at a rate of approxi- 

 mately three-fourths of a centimeter per day; in other words, it requires 

 about forty days for the mycelium to grow through 1 foot of soil. The 

 results ofTer little hope of maintaining in the greenhouse a temperature 

 very unfavorable to the growth of the fungus. 



Table III. — Effect of Temperature VariatioJi on Rate of Mycelial Growth 



in Soil. 



Temperature, Centigrade (Degrees). 



Number of 

 Measurements. 



Daily Growth 

 in Centimeters. 



5, 



8.5, 



14, 



16, 



21-22, 



23-25, 



25, 



25-26, 



25.5-26.5 



26-27, 



30, 



32-3o, 



37.5, 



10 



10 



20 



150 



170 



170 



130 



90 



30 



25 



40 



30 



10 



Effect of freezing the Mycelium . 

 It is very important to know whether soil can safely be used in the 

 benches after being frozen out of doors. The following tests were made 

 to determine this point : — 



Method. — Eight bottles, each containing 33 cubic inches of soil, were plugged, 

 sterilized and inoculated with Cylindrocladium. After seven months the soil was 

 thoroughly infested with the fungus, and probably contained all modifications 

 of the mycelium which ever occur in the soil. Transfers were made and the fungus 

 in all found to be alive. Thap, before the ground froze in November, four of the 

 bottles were exposed outside, one on top of the ground, one just under the surface, 

 one 6 inches down, and one a foot below the surface. The other four were kept in 

 the laboratory for controls. Some of these bottles were brought in each month of 

 the winter to see whether the fungus was still alive. 



