3 6 4 



BOTANICAL GAZETTE 



[NOVEMBER 



ventures prove successful, we may hope for an interesting body of 

 scientific information to come from the study of bog sections. The 

 work of ANDERSON, LAGERHEIM, SERNANDER, WEBER, and others 

 in Sw r eden and Germany, gives indication of the data concerning 

 postglacial migrations of plants and animals, and climatic changes, 

 which will be obtainable when our bog deposits become of economic 

 importance. 



FIG. 4. Diagrams illustrating three stages in the development of peat and mar 

 deposits in lake basins. In drawing the figures it has been assumed that the rates of 

 marl and peat deposition are approximately equal. The peat accumulates most rapidly 

 on the western side of the basin. On the east side a common effect of wave action is 

 illustrated. The process of peat formation is hindered, while that of marl deposition 

 goes on until the aggradation of the bottom reduces the force of the waves sufficiently 

 to allow the bog plants a foothold. A represents conditions in early postglacial times 

 when these basins acquired their first flora. The several plant societies represented 

 are (i) conifer (2) bog shrub, (3) bog sedge, (4) aquatic, the outermost division of 

 which is the chara association. In B the conditions for the growth of plants belonging 

 to the northeastern conifer forest formation have reached their optimum. C repre- 

 sents present conditions in southern Michigan. The plants belonging to the south- 

 eastern broad-leaved forest formation, being climatically favored, occupy the areas of 

 mineral soils, while the conifers are almost restricted to bog areas. 



