Vegetation of Northern Cape Breton. 289 



western Connecticut (see Nichols, '13), is enlightening. The 

 hemlock is capable of growing in a suppressed condition under 

 the shade of other trees for more than a century. A tree which 

 has been thus suppressed may have attained at the end of a 

 hundred years a diameter of perhaps six or eight inches and 

 may have grown well up into the forest canopy overhead. With 

 the improvement of light conditions, which may be accomplished 

 either through its own upward growth or through the down- 

 fall of contiguous trees, such a tree grows vigorously, and 

 may attain an age of more than 300 years, with a diameter of 

 more than four and a height of more than a hundred feet, 

 before its death is brought about through disease, wind, or other 

 agency. What is said of the hemlock applies also to the sugar 

 maple and beech, although these trees are perhaps more 

 susceptible to disease than the hemlock. The behavior of the 

 balsam fir is in marked contrast. Although, like the hemlock, 

 the balsam is able to grow for many years in fairly dense shade, 

 it is handicapped by its susceptibility to fungus diseases, largely 

 in consequence of which its lease on life is limited. At the 

 age of a hundred years, a hemlock, even if it has been grow- 

 ing suppressed all this time, will usually have a sound, healthy 

 trunk. In northern Cape Breton, at any rate, the balsam fir, 

 even under favorable conditions, seldom reaches the age of 

 seventy years without having become infected by heart rot,^ 

 and by the time it has rounded the century mark its trunk usually 

 has become badly rotted within. In addition to the "ground 

 rot," which, in conjunction with the brittleness of the wood, 

 renders the tree liable to windfall (Fig. 13), the balsam fir, 

 when growing in a suppressed condition under hardwoods, is 

 likely to be affected by "top rot," which may cause it to die back 

 from the top. Like the hemlock, however, a balsam may ulti- 

 mately find an opening in the forest canopy overhead. But by 



* According to Zon ('14), two species of fungi are concerned: Trametes 

 P'nii (Brot.) Fr. and Polyporus Schweinitzii Fr., which may cause either 

 "ground rot" or "top rot." According to the observations of Dr. G. P. 

 Clinton in the western Adirondacks, and of the writer in northwestern 

 Maine and northern Cape Breton, in these regions heart-rot in the balsam 

 fir seems to be attributable to still another fungus, Fames piiiicola Fr., a 

 species which Duggar ('09, p. 467) has also mentioned as one which 

 causes disease in the balsam. 



