2) NUStrAlM om SOUEmetm: 
2.) alsopical: 
Regions were separated along 2sotherma/ lines. 
Data more or less arbitrary periods, not for growth and. 
reproduction period. 
Biothermal lines or biotherms more accurate. 
lite Zones and “reas: 
Lines of stress due to heat Lines of stress due to rain- 
fall or drought. 
Arctic or Arctic- 
Boreal Alpine Zone. 
region })Hudsonian Zone. 
@anadian Zone. 
Alleghenian Area 
Arid Transition Area 
( 
Transition Zone | 
Pacific Coast Transition Area 
ise 
Austral | 
arolinian Area 
Upper Sonoran Area 
( Austroriparian Area 
4 
Lower Austral Zone 4 
L Lower Sonoran Area 
J y a 
ee pper Austral Zone 4 
( Humid tropical 
Mroprcal mes Ones. ween cen: 
tl Arid tropical 
The great lines of stress. 
Heat and moisture. 
Lesser dines of stress. 
I. Small bodies of water. 
2, Syoneaas. 
3. Variations in physical and chemical conditions. 
4. Minor variations in physiography. 
Total heat as limiting factor in north and south distribution of 
plants and animais. 
1. Animals and plants limited in northward distribution 
by sum total of effective heat. 
30 
