PATHOLOGY OF THE JACK PINE. 



was marked "infected." Four trees specifically studied yielded by 

 actual count an average of 220 burls 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 age and type 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 li to 2 inches. 



