40 Levi Otto Gratz 



VII was of slightly different consistency, as only incipient wilting was 

 observed in the soil with a moisture content of 17 per cent, while in the 

 other trials permanent wilting resulted at this low moisture content. In 

 trial VIII, tank 3 (table 11), the greatest rate of damping-off was observed 

 in the soil where the moisture content was 18 per cent. This was due to 

 the fact that the plants had started to wilt and were given a small amount 

 of water several da} r s previous to inoculation. The total amount of 

 moisture in the culture vessel was not in excess of the required amount, 

 but the immediate area surrounding the seedlings had an excess as com- 

 pared with the previous experiments. This was a favorable condition for 

 fungus growth. In most of the experiments a soil with a moisture content 

 of 51 per cent caused a delay in the rate of damping-off. This was almost 

 at saturation and a detrimental effect on the host was also noted. In 

 trial X (table 13) an error was made in the original calculation, and conse- 

 quently two moistures were obtained where permanent wilting occurred. 

 The redeterminations at the end of the experiment indicated just what 

 these moistures were. In trials X and XI (tables 13 and 14), the low 

 temperature was maintained by packing snow in one end of the tank. 

 The heater was also in operation to prevent any undercooling. The 

 uniformity of temperatures maintained is indicated in figure 9. 



In all the preceding experiments, none of the check plants developed 

 the disease. 



Good growth of the host was observed at all temperatures between 

 15° and 30° C. Temperatures below 15° slightly decreased the rate 

 of growth, but it was only at the lowest temperature (5.5° C.) that the 

 plants made very little growth. Even at that temperature the plants 

 were in a very thrifty condition at the end of the experiment. Above 

 30° C. the growth was rapid, but the plants were not so intensely green 

 in color as at the lower temperatures, and they showed clearly the effects 

 of the abnormal environmental conditions. 



The following conclusions are to be drawn from these temperature- 

 moisture experiments: „ 



1. A temperature of approximately 7° or 8° C. is the minimum for 

 damping-off of cabbage seedlings caused by Corticium vagum, as a small 

 number of diseased plants were obtained at 10° C. and none at approxi- 

 mately 5.5° C. (tables 13 and 14). 



2. A temperature of 31° to 32° C. is the maximum for the destructive 

 action of the fungus (tables 9, 13, and 15). 



3. There is no sharply defined optimum, but a rapid rate of damping-off 

 may occur at any temperature from 15° C. to 30° C. There is a decrease 

 from these temperatures until the respective limits are reached (tables 

 9 to 15). 



