DRY-ROT OF INCENSE CEDAR. 



33 



a strong bearing on the development of cull cases and the percentage 

 of cull. 



Since neither the total number of infections nor cull cases follows 

 the same law as the percentage of cull, it is self-evident that there 

 must be an exact relation between this last and the more extensive 

 or severe cull cases. Accordingly, in Table IV the severe cull cases, 

 that is, those cases in which one-third or more of the total volume of 

 the tree is a loss through dry-rot, are considered separately. The 

 same basis is used as in Tables II and III and the percentages are 

 based on the number of trees in the dominant and suppressed groups 

 considered separately in each age class. 



Table IV. — Relation between dominant and suppressed trees in severe cull cases found in 

 incense cedars of the combined areas. 



Age class. 



Severe cull cases (per 

 cent). 



Age class. 



Severe cull cases (per 

 cent). 





Dominant. 



Suppressed. 



Dominant. 



Suppressed. 









 

 2 

 2 

 14 

 31 

 48 



281 to 320 years 



71 

 67 

 100 



66 







 3 



2 



5 



26 



73 



321 to 360ryears 



81 



81 to 120 years 



361 to 400 years 



50 



121 to 160 years 



401 to 440 years 



100 





Combined 







201 to 240 years 



14 



17 



241 to 280 years 











In Table IV is seen the same form of progression for the severe cull 

 cases as was shown for the amount of cull in Table II. Low per- 

 centages in both groups up to an age of 160 years, with a sudden 

 increase in the percentage of severe cull cases in the age class of 161 to 

 200 years for the suppressed group are followed by a like increase in 

 the class of 201 to 240 years for the dominant trees. After 240 years 

 is passed there is a higher percentage of severe cull cases for the sub- 

 sequent age classes in the dominant group, just as is the case for the 

 percentage of cull. The only exception to this is found in the class of 

 321 to 360 years, where the relation is reversed. 



The outstanding fact shown by Tables II, III, and IV is that incense 

 cedar during the earlier stages of its life, even though heavily infected, 

 is able to retard the progress of the dry-rot fungus in causing decay. 

 Then comes a period, earlier in the case of suppressed than of domi- 

 nant trees, at which the progress of the fungus can no longer be held 

 in check and the trees become subject to severe decay, with the accom- 

 panying high percentage of cull. In other words, the decay becomes 

 extensive. This period occurs in the age class of 161 to 200 years in 

 the suppressed group and in the age class of 201 to 240 years in the 

 dominant group. An analysis of the individual trees, in a table which 

 is too long to present here, reveals the fact that this change begins at 

 167 years in the suppressed and at 214 years in the dominant trees. 



