MISTLETOK INJURY TO CONIFERS. 3 
The results in Table I, although based on a relatively small number 
of trees, prove quite conclusively the effects of mistletoe on the 
growth of its host. They are graphically shown by the accompany- 
ing series of illustrations (figs. 1 to 4). 
A glance at these graphs shows that although there is considerable 
fluctuation in growth, the line of the uninfected rarely falls below 
that of the infected trees. 
These results are not at all surprising when the nature of mistletoe 
injury is thoroughly appreciated. In a heavily infected region, 
where all species and ages are more or less involved, dead, dying, or 
MVCPTES 
AVERAGE ANNUAL GROWT//. 
1874 1880 1885 1890 S895 7900 S9O5 49/0 /H3 
YEARS 
Fic. 1.—Graphs showing the average annual growth (in inches) for 40 years (1874 
. to 1915, inclusive) of 50 trees of lodgepole pine heavily infected with mistletoe, 
compared with 50 uninfected trees of the same species for the same period. A, 
Heavily infected trees: Average-age class, 65 years; average height, 35.2 feet; 
average diameter, breast high, 6.3 inches. B, Uninfected trees: Average-age class, 
60 years; average height, 48.5 feet; average diameter, breast high, 7.8 inches. 
weakened mistletoe trees, hastened in their decline by the inroads of 
fungi and insects, are a common sight. If these trees are carefully 
examined with respect to the average possible growth for the region, 
it will be found, as Table I shows, that most of them have died or 
have become irrevocably weakened or suppressed at a time when rapid 
or a normal growth should be taking place. This has been found 
to be true in all regions visited in the Northwest where excessive 
mistletoe infection is common. Infected trees of immature years, 
pole size and younger, may linger along indefinitely if secondary 
agents do not appear and may reach an advanced age, but may not 
attain a merchantable size. Heavily infected and. as a result of this 
