PATHOLOGY OF THE JACK PINE. 7 



the selection of nursery sites, with regard to the topography and 

 prevailing winds of the region. 



With the exception of Peridermium cerebrum and P. comptoniae, 

 few fungi of economic importance attack the living jack pine in 

 the drier parts of its range. On the dry pine barrens of the Lake 

 States the jack pine reaches its normal age without much defect 

 in the wood arising from fungous diseases, although exceptionally 

 old trees of 90 years and more frequently show considerable decay. 

 In mixture with other species in the more moist regions of its range, 

 particularly in parts of northern Minnesota and of Canada, Trarnetes 

 pini (Brot.) Fr. causes considerable heart-rot in trees of 60 years and 

 older. In general, however, this fungus is in negligible quantities. 

 In close stands jack pine prunes readily during its most rapid growing 

 period, forming straight clear stems. The rapid occlusion of the 

 branch knots shortens the danger period for infection by wound 

 fungi. It is principally due to this fact that some of the most serious 

 wood-destroying fungi do not effect an entrance until the tree has 

 reached its period of decline. 



Polyporus schweinitzii Fr., causing a butt rot, is usually in greater 

 abundance than Trarnetes pini, but the percentage of infected trees, 

 even on the more protected soils, is seldom more than 2 to 4 per cent 

 of the stand. The jack pine is a deep-rooted species and unless the 

 root system comes in contact with a hard stratum of clay and gravel, 

 root-destroying fungi are largely a negligible quantity. In this class 

 are Fomes annosus Fr. and ArmiUaria mellea (Vahl.) Quel., which 

 very rarely occur on the jack pine. Only a few isolated and unim- 

 portant infections have ever been recorded by the writer. 



The jack pine does not suffer any material injury from needle 

 fungi. Those that do occur are mostly of a saprophytic nature. 

 Lophoderrnium pinastri Schrad. is found only occasionally. 



On dry soils in open stands the jack pine frequently shows a 

 tendency to form witches'-brooms. The terminal shoot, which is 

 the part usually affected, develops into a thick-matted broom, pre- 

 cluding any further growth in that direction. Trees thus infected 

 usually show a rapid falling off in increment, probably dating from 

 the time when the influence of the parasite was first felt. Another 

 type of broom formation is confined to the lower and older branches 

 and has a similar effect on the growth of the host. These brooms are 

 probably caused by some perennial fungus. In the absence of any 

 fruiting structures the causal organism can not be determined. 



The jack pine in its eastern range is not subject to mistletoe injury. 

 Macoun x reports the occurrence of RazoumofsJcya americana (Nutt.) 

 Kuntze, the lodgepole-pine mistletoe, on the jack pine in Canada. 



1 Macoun, John. Catalogue of Canadian Plants, pt. 3, p. 422. Montreal, 1886. 



