PALEOEOTANY 



187 



ments, leaves, stems, pieces of bark, fruit, flowers, pollen 

 and spores, roots, and even entire plants. These natur- 



FiG. 82. — Diagram illustrating the gradual filling up of lakes by the 

 encroachment of vegetation, and also the stages in the origin of peat and 

 marl deposits in lakes. The several plant associations of the Bog series, 

 displacing one another, belong to the following major groups: (i) O. W., 

 open water succession; (2) M., marginal succession; (3) S., shore succes- 

 sion; (4) 5., bog succession, comprising the bog-meadow (Bm), bog-shrub 

 (Bs) and bog-forest (Bf); and (s) M. P., mesophytic forest succession 

 (C/. Fig. 81.) (After Bray.) 



aIly~become buried in the mud and sediment wherever 

 deposition takes place, and when the deposit becomes 



