22 



BULLETIN 1112, U. S. DEPARTMENT OF AGKICULTUBE. 



Table 16, — The effects of mistletoe on the photosynthetic surface of western yellow 



pine — Continued . 





Total num- 

 ber of leaves 

 in entire 

 crown. 



Leaf surface. 



Ratio of lea.' 

 surfaces. 





Tree No. 



Lower 



portion of 



crown. 



Central 



portion of 



crown. 



Upper 



portion of 



crown. 



Entire 

 crown. 



Ratio of 

 voliunes.i 



103 



159,543 

 1,792,439 

 262, 015 

 837,093 

 419,774 



Square 



inches. 



4,094.1 

 217, 828. 8 



40,910.5 

 218, 438. 4 



50, 960. 3 



Square 



inches. 



19, 400. 4 

 356, 549. 8 



24,983.9 

 198,228.7 

 105,868.9 



Square 



inches. 



32,348.2 

 231,613.4 



44, 427. 4 

 128, 939. 5 

 107,921.4 



Square 

 inches. 

 55, 842. 7 

 805, 992. 

 110,321.8 

 545, 606. 6 

 264,750.6 



1.0 

 14.4 

 2.0 



9.8 

 4.7 



1.0 



104 



7.6 



105. .. 



1.4 



106 



9.0 



107 



.96 







1 In these ratios Tree No. 103 is taken as lonity. 



The average length and width of the leaves in the 10 tufts selected 

 were used in determining the leaf surface for a given section of the 

 crown, and this in turn for finding the total leaf surface of a given 

 tree. Table 16 shows that not only does the mistletoe shorten the 

 length of both leaf tufts and leaves, but it also materially decreases the 

 number of leaf tufts per tree for heavily infected trees when compared 

 with healthy trees of the same age and site conditions, (PL V.)" 

 When two trees of the same size, one healthy and the other heavily 

 mistletoed, are compared — Trees No. 103 and No. 107, for instance — ■ 

 it is seen that it has taken the mistletoe-infected tree more than twice 

 the nmnber of years to reach the same size as the healthy tree. The 

 average ratio of the leaf surface in square feet to the total volume in 

 cubic feet for the healthy trees given in Table 16 is 409.7 compared 

 with 185.5 for the heavily infected trees. 



Trees heavily infected with mistletoe not only have considerably 

 shorter leaves and leaf tufts than healthy trees, but the leaves of 

 mistletoe-infected trees are lighter in color than those of healthy 

 trees, being a yellowish green as compared with the olive green on 

 the healthy trees. Each heavy infection causes a localization and 

 reduction of the photosynthetic or assimilatory leaf surface of the 

 tree, which in turn results in a marked decrease in the rate of growth. 



EFFECT ON LONGEVITY OF HOST. 



A number of permanent sample plots were established on the Coco- 

 nino and Tusayan National Forests by the Fort Valley Forest 

 Experiment Station, in 1909, to determine the rate of growth and 

 decadence, the rate of establishment of natural reproduction, and the 

 effect of various factors upon regeneration on cut-over areas. These 

 plots were remeasured in 1914 and 1919. Some of the plots yielded 

 valuable data on -the amount of mistletoe infection and the resulting 

 mortality on cut- over areas. 



