71 8 Journal of Agricultural Research voi. xn. xo. 



-^v- 



From the foregoing studies it may be concluded that the false mistle- 

 toes are serious agents in the suppression of young forest growth. 

 Moreover, young growth once infected on the main stem (and it is 

 usually so infected) can not recover and produce merchantable material. 

 Suppression in young yellow pine even up to the sapling stage is of 

 serious consequence. Very seldom do such trees ever overcome the 

 early influence. This is also noticeable in trees of dense stands or 

 when overtopped by older classes. The ultimate effect on the growth 

 of the tree is exactly equivalent to lack of light, only worse. In the 

 former case the excurrent growth is arrested, and the tree either 

 develops into one continuous broom or dies; in the latter, a sapling 

 of some merchantable value may result. It is clear that every effort 

 should be made in regions of heavy mistletoe infection ro reduce the 

 infection of reproduction by cutting all infected overtopping trees. 

 Care should be taken to prevent the introduction of mistletoe-in- 

 fected transplants in regions where the parasites do not occur/' Such 

 resfions, for examole, are the Black Hills of South Dakota and several 

 of the southeastern Montana forests. 



SUMMARY 



The height growth of young trees is greatly retarded by mistletoe. 

 The effects to be observed are reduction in the length of the internodes, 

 small dimensions of the terminal buds, and reduction in number. 

 This result is caused by the localization of food materials at the seat 

 of infection. 



To reduce the chances of infecting young growth, all overtopping 

 infected trees should be killed. Infected trees of any age should be 

 killed if possible. Care should be taken that infected trees are not 

 planted in regions w^here mistletoe does not occur. 



PLATE 37 

 A. — Pseudotsuga taxifolia infected with Razoumofskya douglasii. 

 B. — Effect of an inoculation with Razoumofskya campylopoda on the height growth 

 of 6-year-old Pimts jeffreyi. Culture made in a greenhouse at Missoula, Mont. 



5 Weir, J. R. mistletoe; injury to conifers in the northwest. U. S. Dept. Agr. Bui. 360, 39 p. 

 27 fig. 1916. Literature cited, p. 39. 



