4384 BOTANICAL GAZETTE [DECEMBER 
| Populus tremuloides 
: Betula papyrifera 
| Pinus Strobus 
Abies balsamea 
Quercus rubra 
Picea mariana 
a 
Pony Betula lutea 
Pyrus americana 
Wiss 
Lo | Tilia americana 
Acer saccharum 
Wo Tuga canadensis 
Fagus americana 
Fic. 6.— : i : i 
1G. 6.—Forest trees: specific ranges of tolerance with respect to intensity of light 
