1921-22 



DEPARTMENT OF LANDS AND FORESTS 



249 



the decay is well advanced or after the afifected trunk has fallen to the ground. 

 The fruit bodies produce large quantities of spores, microscopic in size, which are 

 liberated from their surfaces, and which, carried by currents of air or other agents, 

 serve to spread the fungus to other trees. Infection of living trees takes place 

 through the spores lodging and sprouting on wounds or dead branches or branch 

 stubs. Infection by butt rot fungi may also take place through contact between 

 diseased and healthy roots, or in certain species through fungus strands that 

 may traverse the soil. 



The amount of loss due to butt and heart rot fungi is enormous; they are 



Fig. 8. — Type IV: Heart rot of balsam ("hemlock rot" of balsam). 



easily the most destructive agents of the forest. Mature stands will show a 

 destruction up to 50 per cent, or more. The butt rots as a rule do not extend 

 more than a few feet up from the ground, but they weaken the trees at their 

 bases and so facilitate windfall. Indeed, most windfalls are due to this cause, 

 so that in a very direct way the butt rot fungi increase the fire hazard in addition 

 to destroying the timber. The heart rots work throughout the merchantable 

 part of the trunks; they may weaken the stems at any level, so that broken 

 tops are frequent, and in time they spoil the entire tree for any purpose. Even 

 after the death of their hosts these fungi continue to be active, and so they are 



