30 MASS. EXPERIMENT STATION BULLETIN 183. 



grow in the laboratory also indicates a wide range in feeding habits. 

 Other kinds of decaying vegetable matter in the soil were not tried, but 

 it would not be surprising if it were found capable of hving on a great 

 number of them. 



Depth of Penetration of the Soil. 

 In the soil isolation tests the fungus was not found below 5 inches, but 

 this was not conclusive, since the method of isolation proved not to be 

 entirely satisfactory, and only a few isolations were made. The soil in 

 the milk bottles was never more than 4 inches deep, but the fungus grew 

 as luxuriantly at that depth as at the surface of the ground. In order 

 to test its ability to penetrate to greater depth, glazed drain tiles 2 feet 

 long were closed at the bottom with an inch of cement, filled with soil, 

 plugged with cotton at the top and sterilized. The soil was then inocu- 

 lated on the surface. Holes had been drilled at regular intervals through 

 the side of the tiles. These were corked, and after the whole was steri- 

 lized the corks were made air-tight and water-tight by covering them 

 with melted paraffin. In order to determine whether the fungus had 

 penetrated to a certain depth a cork at that depth was removed, a portion 

 of the soil next to it transferred to an agar plate, and the hole immedi- 

 ately made tight again, all operations being carried out under aseptic 

 conditions. Unfortunately the soil became dry too quickly, due to the 

 large opening at the top, and it was found necessary to pour more water 

 on to the top of the soil. At this writing the fungus is growing through- 

 out the entire depth of soil in the tiles, and has been isolated from the 

 lowest holes, almost 2 feet below the surface. Whether it was washed 

 down by the water or grew down naturally is not certain, but at present 

 the fungus is growing normally in every particle of soil 2 feet below the 

 surface. If it could be washed down by the water in the tiles, there is 

 no reason why it should not be washed down by water in the rose houses. 

 Judging from these results, and what is known about the penetration of 

 other soil fungi, there seems to be no reason for doubting that the myce- 

 lium may exist several feet below the surface, depending to some extent 

 on the character of the soil. 



Rate of Grouih of the Mycelium. 

 The rapidity with which mycelium grows through soil is dependent 

 on the temperature. The optimum, maximum and minimum tempera- 

 tures for growth were determined for the purpose of finding which tem- 

 peratures in the greenhouse are favorable and which unfavorable to 

 the spread of the fungus. 



Method. — When the milk bottles of infested soil are kept in a dark place the 

 progress of the white mycelium downward can be readily observed through the 

 sides of the bottles. A number of bottles were inoculated, and when the mycelium 

 was well started downward the limit was marked accurately by blue pencil lines 

 around the bottles. The bottles were then placed simultaneously in incubators, 



