36 BULLETIN 360, U. S. DEPARTMENT OF AGKICULTUEE. 



stances, however, it is noted that in some regions Douglas fir, larch, 

 and lodgepole pine first become conspicuously infected at sapling or 

 pole size ; that is. it has required several years for earlier infections 

 to become prominent. In any case, the matter turns on the time of 

 life at which a tree becomes infected.- If seriously infected before 

 pole size is reached, the whole tree will in all probability be a cull 

 and a menace to the forest. If infected during or after pole age, the 

 tree may furnish some merchantable material, but will mature far in 

 advance of uninfected trees of the region. Trees infected during 

 early maturity may not be seriously influenced by the parasite ex- 

 cept that their life functions may be slightly changed by brooming 

 and breakage of branches, thus hastening the period of decline. 

 Cutting old and suppressed mistletoe trees is, of course, a saving in 

 several ways, not only to the future forest, but it is getting the best 

 out of a rapidly declining forest capital. Their destruction, how- 

 ever, does not mean that a great advance is being made in eradicating 

 the mistletoe from the region. It simply lessens the chance of infec- 

 tion for a time. Cutting the old and merchantable infected trees and 

 leaving the younger unmerchantable but infected growth will not 

 answer the purpose of control in regions of heavy infection. Very 

 frequently the removal of only the more merchantable mistletoe 

 trees causes the parasite on the trees that are left to develop more 

 vigorously. Numerous observations show that infected trees of 

 various ages succumb very rapidly to the parasite after a certain 

 percentage of the stand has been cut out. For this reason marking 

 the most seriously infected trees for cutting, with the prospect of 

 the least infected reaching a normal maturity or a state of high mer- 

 chantability, should in many regions be discontinued. The only 

 plan left, then, in many regional units of infection is to practice 

 heavier marking than hitherto employed, or, better still, clean cut- 

 ting. It is believed that a close survey of the forests of each district 

 will result in the discovery that there are units or centers of great 

 infection either for one species of mistletoe or for different species. 



Instances of great regional infection for the Northwest have al- 

 ready been indicated. Strange to say, in some cases these centers 

 of infection are quite sharply defined. It seems entirely possible 

 that if these regions were carefully studied and mapped as to the 

 possible environmental factors governing the vertical and horizontal 

 distribution of the parasite, much practical knowledge would re- 

 sult. If the region should be accessible, the sales policy could be 

 modified, with strong emphasis on the control of the mistletoe, and 

 the knowledge already gained from a detailed study of the region 

 should be available for future forest management. It must be re- 

 membered that the great injury now exhibited by forest growth is 

 the accumulation of many years of unhindered activity by these 



