THE DEVELOPMENT OF COMMUNITIES 



337 



Methods of collecting and identifying remnants of fruits, seeds, and 

 leaves found in the peat have been developed by Swedish investigators 

 represented by Von Post and his followers. As early as 1896, G. 

 Anderson gave directions for collecting and determining peat fossils. 

 For such work it is important that the peat samples never get com- 

 pletely dry. They are to be separated by washing in water. Clearing 

 of the darker peats with a httle nitric acid facihtates the separation of 

 materials. Plant remains Hke seeds, leaves, etc., may then be picked 



10 20 50 40 50 60 70 80 90 100% 

 Fig. 171. — A pollen diagram from deposits in south Germany. {After Bertsch.) 

 Beech (a), birch (6), spruce (c), pine (d), mixed oak (e), and hazel (/). 



out with brush or forceps. For identification of wood, microtome 

 sections are often necessary. 



Pollen Analysis. — Secular changes in the dominant tree vegetation 

 of a region, which often represents the cUmax, are best registered by 

 pollen analysis. Acid peat has the property of preserving various 

 parts of plants, and no structure is more resistant to decay than the 

 cutinized outer coats (exines) of pollen grains. Peat samples are 

 taken at depth intervals of 10 to 20 cm., and their pollen content, 

 analyzed microscopically, yields the so-called pollen diagrams (Fig. 

 171), which give the proportion of each kind of pollen in each layer. 



