316 NINETEENTH REPORT. 



Dissemination and Rainfall: 



The active influence of rainfall as demonstrated by the transfer of 

 the fungus by splashings of water from the soil has already been men- 

 tioned. The significance of the splasliings in this connection is seen when 

 periods following mist-like rains are compared with periods in which the 

 rain was more abundant. The correlation between the amount of rainfall 

 and the appearance of the disease in an uninfected field, was noted under 

 the following circumstances: A second crop of red clover following a 

 first crop which had been badly diseased, reached a height of 7-9 cm. 

 without becoming infected. October 15th this field was carefully exam- 

 ined for the presence of the disease but nothing was found. On October 

 25th many of the lower leaves were found to be infected with the fungus. 

 The weather reports for October indicate the following precipitations : 



Total precipitation, Oct. 1-15 0.34 in. 



Daily average, Oct. 1-15 0.021 in. 



Precipitation, Oct. 17 0.06 in. 



Precipitation, Oct. 18 0.30 in. 



The disease was found in the field October 25th, seven days from the 

 last date. The heaviest rainfall between October 1st and 15th occurred on 

 October 1st, but at this time the plants were hardly out of the ground. 

 The heaviest rainfall of .the month occurred on October 18th, and it will 

 be noted that the disease appeared one week later. The heavy rain of 

 the 18th was probably the cause of the splashing of the infected soil upon 

 the plants, with the resulting infection. 



Experiments on Wind Dissemination of Spores: 



Discussion of the problem: — That the wind is more or less a factor 

 in the dissemination of fungous spores has always been assumed, but 

 little experimental work lias been done to demonstrate this. The carry- 

 ing of the spores of Endothia parasitica (Murr) And. has been suggested 

 by several authors, but it remained for Heald, Studhalter, and Gardiner 

 (1915) to prove this. They obtained spores in large numbers at a dis- 

 tance of 300-400 feet from tlie source of supply, and justify the conclu- 

 sion that they may be carried much greater distances. 



Probably the best way of determining tlie spore carrying capacity of 

 wind of known velocity is by outdoor experiments with spore traps. This 

 was the method used by the above mentioned autliors. In the case of 

 M. sarcinaeforme, however, this was impractical during the summer be- 

 cause of the general distribution of the disease. Any experiment under 

 laboratory conditions is necessarily subject to interpretation because of 

 the difficulty of creating a wind similar to that outdoors; also the absence 



