28 



BULLLETIlSr 1112, TJ. S. DEPARTMENT OF AGBICULTUIIE. 



Table 19. — Record of 1912 and 1915 seed crops for 90 standing western yellow pine trees 

 classified by degree of mistletoe injection and amount of seed crop. 











Amount of seed crop 













Degree of 





















Total 



infection. 





















basis. 





Hea 



vy- 



Good. 



Medium. 



Light. 



None. 







Num- 





Num- 





Num- 





Num- 





Num- 







1912 seed 



her of 



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. 























2 



5.3 



9 



23.7 



27 



71.0 



38 



X 



1 



7.7 











1 



7.7 



4 



30.8 



7 



53.8 



13 



xx 































25.0 



15 



75.0 



20 



XXX 



































16 



100.0 



16 



1915 seed 





































1 



2.8 



2 



5.5 



15 



41.7 



18 



50.0 



36 



X 



















2 



14.3 



5 



35.7 



7 



50.0 



14 



XX 



























4 



18.2 



18 



81.8 



22 



XXX 



































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 



' Weir, James R. Mistletoe Injury to Conifers in the Northwest. U. S. Dept. of Agri. Bui. 360, 1916. 



8 Mmins, E. N. Effect of Fertilization on the Seed of Jeffrey Pine. Plant World, 22: 138-144, 1919. 



5 Engler, Arnold. Einfluss der Provenienz des Samens auf die Eigenschaften der forstlichen Holzge- 

 wSchse. Mitteilungen der Schweizerischen Centralanstalt fiir das forstliche Versuchswesen, Ziirieh, 1905, 

 B. 8, s. 81-236; 1913, B. 10, s. 1-386. 



1" Zederbauer, E. Centralblatt fiir das gesammte Forstwesen, 1912, s. 201. ^ 



