THE WESTERN YELLOW PINE MISTLETOE. 25 
period as a direct result of mistletoe infection. Five yellow pines 
on the same area were also killed by mistletoe during the same period. 
Many of the other trees on the sample plots, although not dead at the 
last examination, were small and stunted; they were making an 
almost inappreciable growth and were very unhealthy in appearance. 
Some of these, which are apparently unable to endure the parasitism 
of the mistletoe combined with a rather adverse climate, will un- 
doubtedly succumb before the remeasurement of the plots at the 
end of the next five-year period. Practically all of the trees which are 
heavily infected with mistletoe are ultimately doomed, since it is only 
a question of the length of time during which they can withstand the 
insidious action of the parasite. 
EFFECT OF MISTLETOE ON MERCHANTABILITY OF TIMBER. 
Although the mistletoe injury to the host results less in the depre- 
_ ciation of the lumber than in the impairment of the vital physiological 
_ functions of the tree, there is nevertheless an appreciable effect on 
the quality of the lumber. The accelerated growth of mistletoe- 
infected limbs, as shown in Tables 12 and 13, results in larger limbs 
which produce knots of a larger size in the lumber that is sawed from 
the boles of the mistletoe-infected trees. The number of knots is 
also increased by the greater number of secondary branches and 
twigs in stem infections. The increased size and number of the knots 
May, in many cases, be sufficient to lower materially the grade of the 
lumber. , 
Mistletoe-infection produces a curly or abnormally grained wood 
and weaker lumber. Wood invaded by the thread-like sinkers of 
the mistletoe is spongy, and is frequently discolored and pitchy,-as a 
result of the resinous flow or bleeding of the trees. The presence of 
mistletoe burls renders a tree more susceptible to wind breakage; in 
addition, it may ruin a portion or all of a sawlog. A seedling or 
sapling whose stem is infected with mistletoe will seidom develop a 
_ bole large enough to yield any considerable quantity of lumber and 
very rarely, if at all, lumber of a high grade. It is therefore evident 
that, aside from the physiologically injurious effect of the mistletoe, 
it also introduces a cull factor in that mistletoe-infected trees produce 
a poorer grade of lumber than healthy trees. 
EFFECT OF MISTLETOE ON SEED PRODUCTION OF HOST. 
Pearson ® has shown that, as a result of a collection in 1909, seed 
from mistletoe-infected black jacks gave a germination of 17 per 
cent below that of healthy black jack, which had a final germination 
of 78 per cent. The present study leads to the conclusion that, 
5 Pearson, G. A. The Influence of Age and Condition of the Tree Upon Seed Production in Western 
Yellow Pine. U.S. Dept. of Agri., Forest Service Cir. 196, 1912. 
