THE WESTERN YELLOW PINE MISTLETOE. oi 
felled trees reported in Table 18 are meager because of the difficulty 
experienced in securing seed from mistletoe-infected trees, owing to 
the sterility of the cones and their failure to develop. In fact, a 
diligent search was made for heavily. mistletoed trees which were 
bearing seed, but very few were found. 
Tasie 18.—Data on the seed production of 64 felled western yellow pine trees classvfied 
according to degree of mistletoe infection. 
| Yield per tree. 
Final Clean Reproduc- E 
Degree of infection. germina- seeds, . [as a Le EO alue Basis. 
tion. per pound. @ones. ~ |Cleansecd.| P= tree. 
oT. em ore fae. fee | tie ae 
Number of | Number of 
1913 collection: Per cent. Number. | Bushels. Pounds. | viable seeds. trees. 
ee ee 2. 14, 473 0.8 1.08 12, 942 43 
i Se eee 84.1 | 14, 385 1.0 1.10 13, 292 2 
i Sac eee 81.7 | 13, 314 5 45 4, 895 2 
9.0.0.1 Wed AE (se a a a 77.0 | 14, 475 3 31 3,455 2 
Mean of x, xx, and xxx i 80.9| 14,058 | 6 | 62 | 7, 052 6 
1915 collection: | | 
Se 53.2 | 12, 156 1.1 . 83 5, 626 1h 
Mean ofx, xx,and xxx... 47.1 | 14,170 9 137 2, 202 4 
| 
The extent and condition of the seed crop on the standing trees on 
the permanent sample plots were under observation from 1912 to 
1916 in order to secure additional data on the effect of mistletoe 
infection on the amount and periodicity of seed production. The 
1912 seed crop was rather light; only a few of the trees bore any 
large quantity of cones. In 1913 there was an average crop, with 
practically none in 1914, while the 1915 seed crop was somewhat 
below the average. 
The records of the 1912 and 1915 seed crops for 90 of the living 
western yellow pines are classified in Table 19 by degree of mistletoe 
infection and amount of the seed crop. The seed crops were arbi- 
trarily classified by the observer as heavy, good, medium, light, or 
none. An analysis of the data shows that the amount of seed pro- 
duction varies inversely with the degree of mistletoe infection. As 
the degree of mistletoe infection increases the amount of seed pro- 
duced decreases until very little, if any, seed is produced by heavily 
infected trees. 
These results are further substantiated by observations of the 
writers covering a period of approximately 10 years. Trees heavily 
infected with mistletoe produce small amounts of seed at such times 
as there are generally heavy seed crops, and at other times practically 
none. The few cones that may occasionally be found on trees 
heavily infected with mistletoe are very often aborted, and are 
frequently infested with a cone insect (Conophthorus ponderosz) ° 
6 Material determined by Office of Forest Insect Investigations, Bureau of Entomology, U. S. Dept. of 
e. 
_ Agricultur 
