36 
BULLETIN 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 younger trees are able to retard the fungus sufh- 
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20 
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ZQ 40 60 eO IOO 20 40 60 QO ZOO 20 40 60 60 30Q ZO 40 60 00 400 
Age - years 
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 which 
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 
