36 



BULLETIX 871. U. S. DEPARTMENT OF AGRICULTURE. 



any possibility that when once infected sooner or later some cull 

 will not result. 



To make the relation just discussed even more apparent the 

 four sets of data have been plotted in figure 2. From this, it can 

 be seen that the form of the curves for severe cull cases and cull 

 are the same, but differ quite markedly from the curve for infections. 

 This shows clearly that infections alone are not the sole influence 

 on the development of the dry-rot fungus, for if so the curves would 

 have the same form. The slow progress of the dry-rot in the younger 

 trees is very apparent. 



The curve for the cull cases is somewhat intermediate, at first 

 inclining toward the severe cull cases and later coinciding with the 

 infections. The vouno;er trees are able to retard the fmisus suffi- 

















































































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Age - /ears 

 Fig. 2. — Relation of the age of incense cedar trees to infections, cull cases, severe cull cases, and cull. 



ciently to prevent many of the infections from developing into cull 

 cases, but later this characteristic is obscured. 



The relative percentages of cull due to dry-rot on the various 

 areas is not of importance from the standpoint of the present inves- 

 tigation. That this will vary widely even within the optimum and 

 intermediate ranges is self-evident to anyone who has been on 

 logging operations where incense cedar is being cut. At times the 

 variation, even in localities quite close to each other, is surprising. 

 On the intermediate area the cull for all the trees amounted to 20.5 

 per cent, while for the optimum area the figure was 16.8 per cent. 

 These figures must not be taken as absolute, since it must be remem- 

 bered that the areas were not clear cut. Practically every tree 

 between the ages of 100 and 240 years was cut except those in winch 

 it was apparent that the age could not be accurately determined. 

 Not all the trees below 100 years or over 240 years were cut, how- 

 ever, since this would have meant an enormously increased cost 





