32 BULLETIN 871, IT. S. DEPARTMENT OF AGRICULTURE. 



Table III shows that the percentage of infections is not in exact 

 relation to the percentage of cull caused by dry-rot as given in Table 

 II. In the age class of 41 to 80 years, while the percentage of 

 infections is higher in the dominant trees the percentage of cull is 

 slightly lower. In the age class of 81 to 120 years these percentages 

 bear the same relation to each other as they do in all other classes 

 except the classes of 121 to 160 years and 361 to 400 years. In the 

 former there is a much higher percentage of infections in the dominant 

 trees, while the percentage of cull is equal, and in the latter the per- 

 centage of infections is the same in both dominant and suppressed 

 trees, while the percentage of cull is higher in the former. For all the 

 age classes combined the percentage of infections is markedly higher 

 in the dominant than in the suppressed trees. 



Now, considering the columns relating to the total trees with cull 

 cases, that is, where infections cause a measurable amount of decay, 

 it is found that in the age class of 41 to 80 years none of the infections 

 in the dominant trees result in cull cases, while all of the infections in 

 the suppressed trees do, thus accounting for the higher percentage of 

 cull in the suppressed trees in that class. In the next age class (81 

 to 120 years) the dominant trees have almost twice as many cull cases 

 as the suppressed, and the percentage of cull is just twice as great in 

 the former. But in the age class of 121 to 160 years, while the cull 

 cases are in a higher percentage in the dominant trees the percentage 

 of cull is equal in the two classes, showing that there is more loss per 

 cull case in the suppressed than hi the dominant trees. In the subse- 

 quent age classes the cull cases and the percentage of cull are in the 

 same general relation except in the age class of 361 to 400 years, 

 where the difference is the same as explained for the infections. The 

 total cull cases for the suppressed trees is only 1 per cent higher than 

 for the dominant trees. 



The idea might have been advanced that since inoculation by 

 spores of any wood-destroying fungus is to a certain extent a matter 

 of chance, the greater percentage of cull in the suppressed trees might 

 have been due to a greater number of infections in these trees. But 

 Table III shows more infections in the dominant trees, while the cull 

 cases are about equal in both. Therefore the cull cases must be 

 more severe in the suppressed trees. 



The infections, or even the cull cases, do not show the same pro- 

 gression through the age classes from the youngest to the oldest as is 

 shown by the cull percentage. In the former the sudden, sharp 

 increase in the age class of 161 to 200 years for the suppressed and in 

 the class of 201 to 240 years for the dominant trees is not apparent. 

 The increase is more regular throughout, thus indicating that there 

 is an influence other than merely the number of infections which has 



