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 (EcMnodontium 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 TieterophyUa) , 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 



