28 BULLETIN 1112, U. S. DEPARTMENT OF AGRICULTURE. 
TABLE 19.—Record of 1912 and 1915 seed crops for 90 standing western yellow pine trees 
classified by degree of mistletoe infection and amount of seed crop. 
Amount of seed crop. x 
Degree of Zi Total 
infection. ; basis. — 
Heavy Good Medium Light None : 
Num- Num- Num- Num- Num- 
1912 seed| berof | Per ber of | Per ber of | Per ber of | Per ber of | Per 
crop: trees. cent. | trees. cent. | trees. cent. | trees. cent. | trees. cent. | Trees. 
Osctecee 0 0 0 2 5.3 9 23.7 27 71.0 38 
8 ee ee 1 Weil 0 0 1 Tek + 30.8 7 53. 8 13 
2.0. RY eae 0 0 0 0 0 0 5 25.0 15 75.0 20 
RIK EG sic 0 0 0 0 0 0 0 0 16} 100.0 16 
1915 seed 
crop: 
On scket 0 0 1 2.8 2 5.5 15 41.7 18 50.0 36 
5. oe 0 0 0 0 2 14.3 5 35.7 7 50.0 148 
mide 0 0 0 0 0 | 0 4} 18.2 18} 81.8 22 
xxx, 0 0 0 0 0 0 0 0 18; 100.0 18 
A similar deterrent effect of mistletoe on the seed production of 
Douglas fir, western larch, and lodgepole pine has also been found by 
Weir” to obtain in the Northwest, where seed collected from very 
old mistletoe brooms showed a germination on an average of 10 per 
cent below that of seed taken from uninfected branches of the same 
trees. Munns ® reports that Jeffrey pine trees infected with mistletoe 
had half as many more seed to the pound as were found in the cones 
on thrifty trees, but the germination was 20 per cent lower and the 
seedlings produced were not so vigorous. It seems very improbable 
that moderate or heavy mistletoe infection would ever act as a 
stimulus upon seed production, because its slow, insidious action 
makes constantly greater demands upon the vitality of its host. 
Trees moderately or heavily infected with mistletoe are therefore of 
little or no value for the purpose of seed production. 
The fact is fundamental in silviculture that variations in the indi- 
vidual characteristics of the parent trees are hereditarily transmitted 
through the seed. The extent to which the origin of the seed influ- 
ences such characteristics as the resistance or immunity to disease, 
the rate of growth, and the growth-form of the regenerated forest, 
is of vital importance in the rational practice of scientific forestry. 
The experiments of Zederbauer *° indicate that trees grown from 
seed collected from intermediate, suppressed, and weakened trees 
are less resistant to disease than trees grown from seed produced by 
dominant and vigorous trees. The hereditary characters of the spe- 
cies are not changed materially during one rotation. Several gener- 
ations are necessary to show the true effects of those characteristics 
7 Weir, James R. Mistletoe Injury to Conifers in the Northwest. U.S. Dept. of Agri. Bul. 360, 1916. 
8Munns, E.N. Effect of Fertilization on the Seed of Jeffrey Pine. Plant World, 22: 138-144, 1919. 
9 Engler, Arnold. Einfluss der Provenienz des Samens auf die Eigenschaften der forstlichen Holzge- 
wiichse. Mitteilungen der Schweizerischen Centralanstalt fiir das forstliche Versuchswesen, Ziirich, 1905, 
B. 8, s. 81-236; 1913, B. 10, s. 1-386. * 
10 Zederbauer, E. Centralblatt fiir das gesammte Forstwesen, 1912, s. 201. 
