20 CKANBERRY DISEASES. 



have been kept in a refrigerator at a temperature of about 3° C. 

 The cultures kept in the laboratory made the most rapid and vigorous 

 growth of mycelium, those in the thermostat and refrigerator grow- 

 ing about one-half as fast. All these cultures finally produced 

 pycnidia. but no signs of asci were ever found. 



Experiments have also been tried to determine the effect of differ- 

 ent quantities of moisture. The fungus was found to grow more 

 rapidly on a rather wet medium, but there is no indication that this 

 influences the production of the ascogenous stage of the fungus. 



Other experiments were tried to determine the effect upon the 

 growth and development of the fungus of varying the amount of 

 available air and the evaporation by plugging the culture flasks more 

 or less tightly. Little or no difference was noticeable in the growth 

 in these flasks, and only pycnidia Avere produced. 



The work of Blakeslee -" on Mucor and the factors controlling the 

 production of zygospores in that and related genera has suggested 

 the possibility that the sexvuil or ascogenous fructification might 

 arise from the union of different races or individuals. The few 

 experiments Ave haA'e made along this line, however, have been 

 unsuccessful. 



It has been thought b}^ Brefeld -^ that ascus formation may depend 

 upon the time of the year, or possibly the period of development of 

 the fungus in its host. Our iuA^estigations, however, are not conclu- 

 sive in regard to these points, so far as they concern Guignardia 

 raccinii. Cultures liaA^e been made from fruit and leaves taken 

 almost everA' month during the Aear. and it AAill be noted that cul- 

 tures Avhich produced the ascogenous stage of the fungus AAere made 

 in JanuarA^, March, May, and December. Many other cultures, hoAV- 

 GA'^er, made during these same periods and from leaves and fruit in 

 AA'hich the fungus had presumably passed through approximately 

 the same period of deA-elopment Avere either sterile or produced 

 pycnidia only. While we have no cultures made from material taken 

 during the simimer AA'hich have produced ascospores, this may be 

 due to the fact that comparatiA^ely feAv cultures haA^e l>een made from 

 leaA'es or fruit during that season. 



In regard to the bearing of the duration of development of the 

 fungus upon the j^roduction of asci, we haA^e no means at hand of 

 determining, except by mere conjecture, the age of the fungus Avhich 

 may be present at any j^articular time in the tissues of cranberry 

 leaA'es or fruit, not knowing positiA-ely AA'hen the infection took place 

 :rnd the germ of the fungus entered the plant. All the evidence at 

 hand. hoAveA'er, points toAA'ard June and July as the time. 



As a result of our Avork, we are led to the belief that there is some 

 inherent potentiality in the mycelium of the fungus in certain strains, 



110 



