MICHIGAN ACADEMY OF SCIENCE. 321 



The spores germinate readily in water. In clover juice large swellings 

 at the base of the germ tubes ai)pear, and new spores are formed within 

 five to seven days. In five per cent dextrose solution the spores in some 

 cases produce large, bud-like swellings resembling a young spore. This 

 may be a trend toward an Alternaria habit. 



The fungus grows well upon a large variety of culture media, with- 

 out striking modification, except, perhaps, the dearth of spores on potato 

 plugs, on which growth is otherwise well developed. Sugar seems to 

 favor spore production. 



In media containing nitrogen, ammonia is one of the end products of 

 metabolism. No acid or gas is produced in glucose, maltose, and 

 saccharose solutions. 



The fungus grows at temperatures from 6° C. to 37° C, but at the 

 latter temperature spores are not produced. The thermal death-point of 

 the spores, wet heat, lies between 59° C. and 60° C. for 10 minutes. 

 Dry spores are not killed by one hour's exposure at 75° C. (dry heat). 

 Germinating spores are killed by exposure of 10 minutes to 45 to l'8l/2° C. 



The spores require an air humidity of 92.8 to 93.4% saturation before 

 they can germinate. The spores will not germinate if the saturation 

 is below 92.8%. The spores can withstand dessication for a long jjeriod 

 of time, at least for 18 months, and probably very much longer. 



The fxmgus grows equally as well in light as in darkness. The shaded 

 lower leaves of the plants are more readily attacked than those well 

 lighted. 



In culture, the fungus produces a toxic substance. The results of this 

 phase of the investigation have already been summarized on page 313. 

 Marked attenuation was found in an old culture of the organism. 



The disease-producing organism may spread from the soil to the plant 

 as a result of splashing by the rain. The fungus probably lives over 

 winter on the trash from a diseased crop. The ascent of the disease 

 upward from the lower leaves seems to be co-ordinated with the amount 

 of precipitation. The spores of M. sarcinae forme have been found in 

 red clover seed but not growing upon it. This is a possible means of 

 disseminating the disease. Experiment has shown that the spores can 

 be carried at least 14.6 meters (48 feet) by a wind with a velocity of 3.93 

 miles per hour, and it is very probable that outdoors, because of the 

 higher altitude obtainable, they may be carried a greater distance, 

 sufficiently far to reach and infect other fields. 



The ultimate method of controlling this, and other clover diseases, 

 must be on the breeding of resistant varieties. 



