66 Forestry Quarterly. 



Hemlock is found nowhere north of 55°, and finds its Hmits 

 mostly at 58°. 



Chestnut, Tulip, Black Walnut, Sycamore and Sassafras are 

 practically confined to the Ontario peninsula south of 62°. 



Butternut and White Ash (Fraxinus americana) are found 

 chiefly south of the isotherm 60°, but push up to 58° in Maine 

 and New Brunswick. 



With reference to the tetrahoral isotherms Canada's Atlantic 

 flora may be roughly divided as follows : 



1. Northern border of Southern Hardwood Forest, isotherm 

 62°. 



2. Transition zone of mixed Hardwoods and Conifers, 62° to 



56°. 



3. Northern Coniferous Forest, 56° to 50°. 



It may be concluded that in Eastern Canada, temperature is 

 controlling climatic factor for forest types, but not for species-; 

 precipitation is practically everywhere abundant; humidity data 

 are not available, but it is safe to say that the moisture content of 

 the air is ample (except tundras). 



