THE WESTERlsr YELLOW PINE MISTLETOE. 25 



period as a direct result of mistletoe infection. Fire 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 mthstand 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 Imnber. 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 seldom 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 germ in ation 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. 



