160 FOREST PROTECTION 



This observation is backed by the facts exhibited near Ducktown, 

 Tenn., where the shade trees in the gardens seem to do re- 

 markably well in close proximity to the smelters. 



Ceteris paribus, the following schedule has been arranged as the 

 result of investigations for the trees in the Ducktown region 

 having over 7" diameter, the trees most easily killed by SO, 

 being placed at the top of the schedule: 



Susceptibility to Actual Injury. 

 White Pine 

 Hemlock 

 Scrub Pine 

 Pitch Pine 

 Birch 

 Chestnut 

 Hickory 

 Oaks 



Yellow Poplar 

 Maple 

 Black Gum 



This schedule tallies well with the schedule given by European 

 authors for closely related species. 



If a similar schedule is formed according to the ease of discolor- 

 ation, entirely different results are obtained: 



Susceptibility to Discoloration. 



VERY easily medium NOT APT TO BE 



DISCOLORED DISCOLORED DISCOLORED 



Black Oak Poplar Black Gum 



Hickory White Oak White Pine 



Scarlet Oak Chestnut Oak Maple 



Chestnut Post Oak Pitch Pine 



Spanish Oak Hemlock 



Noteworthy it is that the power of resistance to fumes is more 

 increased by the power of reproduction than decreased by 

 the sensitiveness of the leaves. 



In nature, wherever grave deviations from exact schedules of sen- 

 sitiveness are found, it stands to reason that other influences, 

 aside from sulphurfumes, are simultaneously responsible for 

 the death or for the discoloration of the trees. 



The best time for any observations in the forest is the late sum- 

 mer or early fall (the time between August 15 and October 1). 



Sulphurfumes cannot be held responsible for the local death of 

 trees within a "smoke region," 



(1) if species known to be more sensitive are less affected 

 than species known to be more resistent; 



