PATHOLOGY OF THE JACK PINE. 6 



brain — cerebroid. These blisterlike swellings are orange-yellow at 

 first; after the rupture of the peridium and the dispersal of the 

 golden yellow seciospores they become whitish. The gall formation 

 causes great injury to the trunk and branches (fig. 1). The infection 

 usually begins by means of some injury to the bark or cambial layer. 1 

 The gall swellings gradually increase from year to year from the 

 growth of a perennial mycelium, so that they finally encompass the 

 entire branch, resulting eventually, if the galls are near the trunk, in 

 its death below and 

 above the hypertro- 

 phy. Whether or 

 not the entire branch 

 dies depends upon 

 the presence of lat- 

 eral, leafed branches 

 below the gall. 



In dry sandy areas 

 Peridermium cer e- 

 brum confines itself 

 more generally to the 

 branches, occurring 

 rarely on the trunk 

 but frequently in the 

 axils of the branches. 

 This latter condition 

 usually results in a 

 combination trunk 

 and branch gall, 

 which in numerous 

 instances produces 

 greater damage than 

 either of the other 

 two types of galls. 

 The branch and 

 trunk are girdled by 

 abnormal wood 

 tissue and are thus 

 weakened (fig. 2). This results usually in either the branch or the 

 tree being blown down by the wind. Personal observations show 

 that borers and wood-rotting fungi entering at the burl often hasten 

 the decline of the tree. 



From a careful examination of young twigs showing very recent 

 infections at leaf scales, leaf traces, and at the bases of young pistillate 



Fig. 2.— Cross sections of the main trunk of a jack pine heavily in- 

 fected with Peridermium cerebrum. Note the progressive girdling 

 by the resinous burl tissues in the upper figure and its effects on 

 the increment of the trunk below, as shown in the lower figure. 



'• Wounds made by sapsuckers, ovipositors of bark-stinging insects, rodents, and ice and snow breaks 

 are common means of entrance for Peridermium cerebrum. 



