CHESTNUT BARK DISEASE. 441 



the spores the higher the percentage of infection. For instance, 

 on chestnut seedlings, cultures varying from 28 to 55 days old 

 gave successful inoculations varying from 100 to 50 per cent.; 

 while those 79 to 250 days old gave from 30 to o per cent. 

 However, with the latter the time of inoculation may have 

 entered into the problem, since in no case did we try to inoculate 

 on the same date with spores of greatly different ages. 



Time of Inoculation. Inoculations made in the spring are 

 more successful than those made in midsummer, at least those 

 we made in the spring were, as a rule, much more successful 

 than those we made in July. However, as just stated, those 

 made in the spring were made with younger spores than those 

 made later, and just how much of the failure of the latter was 

 due to the time of inoculation and how much to the age of the 

 spores could not be determined. We have also tried inoculations 

 on dormant seedlings in the greenhouse, and these have either 

 failed to take or took only after the trees began to grow. The 

 length of time the fungus has been in culture, age of the spores 

 used, time of year the inoculation is made, are all points that 

 need further investigation to bring out their bearings more 

 clearly. 



Condition of Host. We tried several experiments to deter- 

 mine what effect the condition of the host had on the success of 

 the infection. These experiments included a few plants kept 

 unusually wet and others very dry, in the greenhouse; others 

 severely ridged outdoors to aid in drought conditions, com- 

 pared with plants not ridged; and plants with knife cuts encir- 

 cling the bark (in some cases with a band of bark removed) 

 which were inoculated above and below these injured places. 

 The results were rather conflicting, so that we could not tell 

 whether or not these treatments made any special difference. 

 Inasmuch as they did not show more striking evidence in favor 

 of increased blight development under unfavorable conditions 

 of the host, perhaps they may be interpreted as rather against, 

 than in favor of, our theory that the condition of the host 

 affects the prominence of the fungus as a parasite. However, 

 such experiments need to be made in greater number and during 

 several seasons in order to judge accurately as to results. 



