304 THE STUDY OF PLANT COMMUNITIES * Chapter XI 



ings, particularly regarding climate, in one place with those in an- 

 other. Obviously such studies can not be entirely satisfactory since 

 they indicate vegetation only within the bogs themselves, or at 

 their immediate margins, and bog vegetation is not of the climax 

 type. 



POLLEN ANALYSIS 



When, in 1916, von Post presented the results of his studies ot 

 pollen preserved in Swedish peat deposits, an entirely new ap- 

 proach to the reconstruction of prehistoric vegetation was begun. 97 



EBERBACH , 



" MM— ■ 



FlG. 162. A type of sampler frequently used for pollen studies of peat and 

 marl deposits. It consists of a jacketed plunger that completely closes the 

 sharpened end of the jacket. After it is pushed down to sampling depth, 

 using the four-foot extension rods, it is drawn upward a few inches. This 

 partly withdraws and locks the plunger in the upper part of the jacket. 

 Then, when forced downward, the jacket cuts a ten-inch sample core- 

 Courtesy of Eberbach and Sons Company. 



Wind-borne pollen is deposited everywhere and much of that 

 which falls in a lake is preserved in its sediments because of the 

 low rate of oxidation. Since the pollen of most dominant trees is 

 wind-borne, the pollen deposited at any one time should include 

 that of the important tree species in the general vicinity and the 

 numbers of grains of a species should be indicative of the relative 

 importance of that species in the surrounding forest at the time. 

 Because pollen grains of a species are constant in size and form, 

 genera, and sometimes species, can be identified positively. Conse- 



