BULLETIN 212, U. S. DEPARTMENT OF AGRICULTURE. 



able or unfavorable to the best development and spread of disease. 



The fungi inhabiting the bark and leaves are probably influenced by 



these factors in a far greater degree than are those attacking the 



heartwood. 



Pathologically, the jack pine may be divided, in most regions of its 



range, into two forest types, which are determined largely by the 



amount of moisture in the soil. 

 The fungi at work in the moist or 

 swamp type may occur in the drier 

 and more arid type, but may show 

 considerable variation in the abun- 

 dance of any one species. Another 

 factor of considerable importance 

 is the absence or presence of any 

 associate tree of the type which 

 may prove equally or even more 

 susceptible to cosmopolitan fungi 

 and thus increase the chances of 

 infection for all members of the 

 stand. In many parts of its range 

 the j ack pine occurs in pure stands. 

 In mixture with other species it is 

 usually attacked by a greater num- 

 ber of diseases than in pure stands. 



DISEASES. 



The fungus causing the greatest 

 immediate injury to the jack pine 

 of all age classes, as determined by 

 pathological surveys in Michigan 

 and Minnesota, is Peridermium, 

 cerebrum!* eck (Cronartium quercus 

 (Brondeau) Schrot.). 1 The galls 

 (fig. 1) produced through the stimu- 

 lative effect of the fungus are in 



Fig. 1. — An 18-year-old jack pine infected with -..- -i T i-j_iii 



Peridermium cerebrum, showing the character- May and June COVered With glob- 

 istic swellings which extend around the main oid Swellings Somewhat after the 



stem " manner of the convolutions of the 



1 Peridermium cerebrum is quite similar to P. harknessii Moore, which causes much damage to Pinus 

 contorta (lodgepole pine) in the West. Some recent observations by Hedgcock and Meinecke indicate the 

 possible identity of Peridermium cerebrum with P. harknessii on Pinus radiata (Phytopathology, vol. 3, 

 p. 16, 1913). These two Peridermiums are held by Arthur and Kern to be identical (Mycologia, vol. 6, 

 no. 3, pp. 133-137, 1914). Cultural experiments by Arthur and Kern (Mycologia, vol. 6, no. 3, pp. 133-137, 

 1914) and also by Hedgcock and Long (Journal of Agricultural Research, vol. 2, pp. 247-249, 1914) demon- 

 strate the identity of Peridermium fusiforme with P. cerebrum. Peridermium globosum Arthur and Kern 

 founded on a single specimen and supposed to occur on Pinus strobus has been acknowledged by the authors 

 to be P. cerebrum on Pinus divaricata. The error arose from a misidentiflcation of the host (Mycologia, 

 vol. 6, no. 3, pp. 133-137, 1914). 



