BULLETIN 212, U. S. DEPARTMENT OF AGEICULTUEE. 
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 jack 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 Peck (Cronartium quercus 
(Brondeau) Schrot.). 1 The galls 
(fig. 1) produced through the stimu- 
lative effect of the fungus are in 
May and June covered with glob- 
oid swellings somewhat after the 
manner of the convolutions of the 
Fig. 1.— An 18-year-old jack pine infected with 
Peridermium cerebrum, showing the character- 
istic swellings which extend around the main 
stem. 
i Peridermium cerebrum is quite similar to P. harlnessii 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 radiaia (Phytopathology, vol. 3, 
p. 16, 1913). These two Peridermiums are held by Arthur and Kern to be identical (Mycologia, vol. 6, 
no. d, 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 aul hors 
to be P. cerebrum on Pinus divaricata. The error arose from a misidentification of the host (Mycologia, 
vol. 6, no. 3, pp. 133-137, 1914). 
