Upper photic zone divided into two strata, ebb and flow 
here. 
I. Algae stunted, thick epidermis. 
2. Best for growth. All pelagic seed plants and great 
mass of algal vegetation. 
Lower photic zone divided into two strata with only algae 
found in this zone, different algae in different depths, 
below ebb. 
Green algae. 
Brown algae. 
Red algae, sensitive to light, light decolorizes them. 
XXI. SUGGESTIONS FOR PRACTICAL STUDY OF PLANT 
FORMATIONS 
Student should have had a good course in elementary plant 
physiology and general plant morphology. 
For independent study more required. 
Work of beginning student can be done under the guidance of 
teacher. } 
Students can more easily detect a life relation, than they can 
determine many of the plants. 
District selected for study should include if possible 
Forest. 
Low marshy areas. 
Ponds or lakes. 
These will usually include rocky, sandy, clayey areas, 
ravines, bluffs, meadows, etc. 
Map the region, based on some good topographic map, like 
those being issued by the U. S$. Geological Survey. 
Studies shouid be supplemented by lectures and reading. 
For practical work district selected may be in either 
1. Coastal plain and continental valley district, or 
2. Mountain districts, or 
3. Division of territory recognized in Physical Geography. 
The larger area may be divided somewhat as follows: 
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