28 BULLETIN" 871, U. S. DEPARTMENT OF AGRICULTURE. 
serious cull case traced to a healed fire scar. This wound healed 
when the tree was 38 years old; hence infection could not have 
occurred subsequent to that age, since the field notes seem to exclude 
any possibility of an entrance of the dry-rot through a knot. Numer- 
ous other examples might be cited, but none of them reduces the 
minimum age of possible infection below 38 years. 
An analysis of infections definitely traced to healed wounds in 
trees on the optimum area places the earliest age at which trees may 
be infected at 34 years, and this may be accepted as the age of infec- 
tion for all the areas, since there is no apparent reason other than 
chance as to why the various areas should differ in this respect. 
Infections were very common between the ages of 45 and 80 years. 
No tendency was apparent toward an earlier age of infection in 
suppressed than in dominant trees, or vice versa. The foregoing 
figures are based on an analysis of 99 infections. Of course, this age 
may be even lower than here indicated, but it is evident that the 
earliest age of infection can not be lower than the age at which heart- 
wood formation takes place in incense cedar. Just when this occurs 
is not definitely established, but observation seems to place it some- 
where around 20 to 30 years. To be sure, there is a possibility of 
infection taking place in pathological heartwood resulting from an 
injury before the true heartwood is formed, the fungus mycelium 
vegetating in this type of heartwood until such time as true heart- 
wood develops and then attacking it. While absolute proof of this 
course of procedure is lacking, observations have all tended toward 
substantiating the theory. 
Furthermore, this age agrees approximately with that found by 
other workers with different species. Meinecke (16, p. 47) finds 
that for white fir (Abies concolor) decay caused by the Indian-paint 
fungus (Ecliinodontium tinctorium) "may show in trees 60 years old 
or perhaps younger," while Weir and Hubert (32, pp. 17-18), working 
with the same fungus in western hemlock (Tsuga JieteropJiylla) , set 
the average infection age for one type at 44.5 years and for another 
at 57.3 years. The figures are obtained by the use of a formula 
applied to the younger age classes. These same workers (33, pp. 
11-12) place the "age of earliest infection" at about 50 years for 
western white pine (Pinus monticola) attacked by several common 
wood-destroying fungi. 
Interesting as the determination of the age of infection or the age 
of earliest infection may be from an academic viewpoint, it is of little 
practical importance in this region. The questions of real import 
in this as in other species are the age at which decay begins to result 
in cull of economic importance and whether there is any relation 
between this and dominant and suppressed trees. The trees on the 
intermediate area and on the optimum area were first arranged 
