ROSE CANKER AND ITS CONTROL. 



21 



Table II. — Germination of Spores after Exposure to a Temperature of 

 40° C. 



It will be noticed that the longer the period of exposure, the longer the 

 time required for germination after being removed to room temperature. 

 There was n« decrease in the percentage of germination until after four 

 hours. From this point it dropped rapidly to less than 1 per cent, in 

 six and one-half hours, and no germination whatever after seven and one- 

 half hours. 



Effect of Desiccation on the Spores. 



The length of time during which spores are able to live in a dry condi- 

 tion may have an important bearing on dissemination of a fungus and 

 spread of a disease. Neither the thinness of the walls nor character of the 

 spore contents of Cylindrocladium would lead one to expect great lon- 

 gevity. The following method was used to determine longevity at 

 ordinary room humidity : — 



Method. — The lids of Petri dishes, containing pure cultures of Cylindrocladium 

 with abundance of conidia, were lifted enough to allow the thin film of agar to 

 become hard and dry within a day or two. At intervals of one day .spores were 

 transferred from these dishes to drops of water on slides in Petri dishes, as pre- 

 viously described for other germination tests. The percentages of germination 

 were determined after the spores were kept in moist chambers for twenty-four 

 hours. All checks — made from the cultures before tilting the lids — germinated 

 to over 95 per cent. Several hundred spores were transferred for each test. Three 

 different Petri dish cultures were used at different times. 



In every trial the percentage of germination began to* decUne after 

 twenty-four hours. In two days it had dropped to 25 per cent.; in five 

 days, to 10 per cent. After ten days not more than 1 per cent, germinated, 

 and in no case was any germination observed after drying for fifteen days. 



