MISTLETOE 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 



FIG. 1. Graphs showing the average annual growth (in inches) for 40 years (1874 

 to 1913, 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 Xorthwest 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 



