194 LABORATORY AND FIELD EXERCISES 



(4) Define a plant association. "What are the most 

 important considerations which determine the 

 kind of dominant species composing the associa- 

 tion you have just studied ? 



2. Kinds of associations. Study the vegetation on the margin 



of a pond, lake, or stream, including the aquatic plants, 

 the plants of the shore, and those of the drier regions 

 adjoining the shore. 



a. Zonotion, Do you note any regularity in the arrange- 



ment of definite types of plants in the water and 

 along the shore ? Are there definite associations of 

 plants thus arranged? Is the arrangement suffi- 

 ciently regular to constitute definite zones of vege- 

 tation ? See the text and figures illustrating the 

 nature of zonation. 



b. Kind and number of species in each zone or association. 



(1) What plants grow in the water ? Are there floating 



and attached algae or seed plants ? What plants 

 grow along the immediate shore line ? Study the 

 species in each zonelike association. Do you 

 find any discrepancy between the habitat and 

 the habit of plants in any given association ? 

 If so, explain. 



(2) Determine the nature of the habitat and the environ- 



mental factors controlling the association of plants 

 in each zone of vegetation under consideration. 

 Observe the structural adaptations of the species 

 in the various zones. 



3. Summary and conclusions. 



a. Draw an outline diagram of the shore line investigated 

 and indicate by symbols (such as circles, squares, tri- 

 angles, crosses, etc.) the different zones of vegetation 

 and the number and kinds of plant associations found. 



