16 



BULLETIN 1112, U. S. DEPARTMENT OF AGEICTJLTUEE. 



In the early stages of the study the trees were segregated by crown 

 classes. Since by far the greater part of the trees in the open park- 

 like stands studied were in the isolated, dominant, and codominant 

 classes, the effects of crown class were found to be negligible in con- 

 trast to the marked effect of mistletoe in retarding the rate of growth. 

 The retardation of growth due to the mistletoe was consistently 

 evident in each age-crown class in which suflB.cient trees were secured 

 to form a comparable basis. It was impossible to secure an equal 

 number or equal proportion of each crown class in each age-infection 

 class. As has been shown, it was found more necessary to segregate 

 the feUed trees by age-infection classes than by crown-infection 

 classes. It was impracticable to segregate by crown classes all of 

 the trees used in this study because of the extremely small number 

 and in some cases entire lack of trees falling into each age-infection- 

 crown class, had such a triple classification been used. The diameter, 

 height, and volume growth during the 5-year period, 1910-1915, in 

 the 21 to 60 year age class of the isolated trees included in Table 7, may 

 be cited to show the injurious effect of mistletoe on growth within a 

 given age-crown class, as follows : 



Degree of infection. 



Breast high 

 diameter 

 growth for 



last 5 years. 



Height 

 growth 

 for last 

 5 years. 



Volimie 

 growth 

 for last 

 5 years. 



Basis. 







Inches. 

 1.3 

 ,8 

 .6 

 (1) 



Feet. 



3.3 



2.0 



1.2 



.5 



Cubicfeet. 



2.04 



.54 



.25 



.004 



Trees. 



3 



X 



2 



XX 



3 



XXX .. . . 



4 







1 The trees in this class were less than 4.5 feet in height. 



In Table 11 is shown increment data for two intensive sample 

 plots aggregating 24 acres, located within the extensive plot on the 

 Tusayan National Forest mentioned below, the data being grouped 

 according to degree of infection. An accelerated growth is noted 

 in the x infection class comparable to that noted in Table 1, the 

 explanation of which is not evident from the data at hand, unless 

 it be an actual stimulation due to the presence of the mistletoe. 

 The decrease in the rate of growth in the heavily infected class is very 

 marked and is in accord with all of the other results secured in this 

 study. 



Two seedlings, one healthy and the other heavily infected with 

 mistletoe, which were growing side by side on a good site, were ana- 

 lyzed and both found to be 15 years old. The healthy seedling 

 showed marked vigor and was 4 feet tall, whereas the one infected 

 with mistletoe was only 3 feet tall and showed evident stunting and 

 that death was imminent. 



