Action of glaciers. 
Limits of glaciers. 
Effect of cold wave on plant migration. 
Forward and backward movement. 
Evidences of plant migration in glacial times. 
a. Distribution of plants in North America, Europe and 
Asia, and relation of flora (trees, algae, fungi, etc.) 
b. Extinction of many in Europe and. preservation in 
North America. 
c. Fossil remains of plants in Arctic regions. 
Present climatic pressures. 
1) velumd tropics. ) Mertility, of ispecies: 
2. te ECC: 
North and south movement meet and produce a 
lateral pressure. 
3. Vicinity of mountains. 
4. Vicinity of arid regions. 
Fertility of aggressive species everywhere. 
Barriers to plant migration. 
re inds of climate: 
2, Kinds of soil: 
3. Discontinuity of land. 
4. Mountain chains. 
Conflict of species in migration. 
XIII. PLANT FORMATIONS 
The General Formations. 
Dominant vegetation type of a region is a formation. 
General formations in 4 divisions. 
1. Climatic Formations. 
Edaphic Formations. 
Aquatic Formations. 
Culture Formations. 
BEN 
1. Climatic Formations, 
Plant covering of earth not uniform. 
Lack of uniformity of climate, topography and soil. 
Moisture 
Pwo climatic factors 2) %: 
i emperature 
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