36 BULLETIN 360, U. S. DEPARTMENT OF AGRICULTURE. 
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 fora time. Cutting the old and merchantzble 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 fer 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 
