16 BULLETIN 1112, U. S. DEPARTMENT OF AGRICULTURE. 
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 sufficient 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 felled 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: 
spe nies a vase 
: : iameter grow owt F 
Degree ofinfection. growth for} for last ie last Basis. 
last 5 years.| 5 years. | 5 years. 
Inches. Feet | Cubic feet Trees. 
OS hed chs aoe we baas «ERE co SRE Esso See aes SE 1.3 3.3 2. 04 3 
>. CS ee a Rae oe ee, PRO RRE pREy ARAL SA 8 2.0 . 54 2 
ERY iste Be oa koe cA iS DE I Se eee oie Se eee .6 1,2 25 3 
BOR ot ee oe. Se ec cas cee ee I ee Suen ee (4) ! 5 . 004 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. 
