PATHOLOGY OF THE JACK PINE. 
was marked "infected." Four trees specifically studied yielded by 
actual count an average of 220 hurls on the branches and 13 on the 
trunks. The cones produced by these trees, although of average 
number, were small, with a higher percentage of abortive sporophylls 
than is commonly the case with this species (fig. 3). Comparative 
germination tests of seeds from heavily infected and vigorous non- 
infected jack pine of the same ago and typo conditions showed for 
the former a germination of 19 per cent below that of the latter. For 
this experiment 10 
samples, consisting 
of a dozen or more 
cones, were taken 
from each of five 
heavily infected and 
five uninfected 
pines. Fifty seeds 
from each of these 
samples were plant- 
ed in sand, kept 
moist with distilled 
water, and allowed 
to stand at labora- 
tory temperature 
(about 70° F.) for 
90 days. 
The prolific devel- 
opment of Periderm- 
ium cerebrum in 
many parts of the 
jack-pine forests of 
the Great Lakes 
region is a factor in 
reforestation which 
should be carefully 
considered. The 
fact that the fungus 
occurs so commonly 
on young seedlings in the natural forest and occasionally in the 
nursery shows that it is a menace to the best development of the 
species. The largest and best formed jack pine in all the regions 
studied where the Peridermium was abundant was almost entirely 
devoid of this injurious disease. However this may be interpreted 
as to the original differences in vigor, the fact that heavily infected 
trees were invariably scrubby and ill formed is, in the mind of 
the writer, directly referable to the effects of the parasite. The 
fact that P. cerebrum has its telial stage on the leaves of several 
Fig. 3. — Branch of jack pine with aborted cones, the result of a severe 
attack of Peridermium cerebrum. Note that some of the cones did 
not open and that most of them are less than an inch in length. 
Average normal cones measure from H- to 2 inches. 
