192 CLIMAX FORMATIONS OF NORTH AMERICA. 



forest of pine, spruce, and fir. This same statement probably holds for the 

 great coniferous areas of Wisconsin, Minnesota, New York, northern Penn- 

 sylvania, and the New England States. Even so far south as northern 

 Indiana, in the sand-dune region, Cowles has shown that where the surround- 

 ing vegetation consists of pines there is no doubt the same order of succession." 



The author simimarizes the results of his study of North American bogs as 

 follows: 



"1. The bog societies are tj^ical of the colder portions of North America 

 and are closely related to the bog societies of Europe and Asia. 



" 2. They show an optimum region of dispersal having a moist climate, sub- 

 ject to very great temperature extremes. Within this region the plants have 

 a greater range of habitats and an increased physical development. 



"3. As we go away from this center, either north or south, the first forms to 

 show the eJBfect of climatic change in diminished size and frequency of occur- 

 rence are the arborescent species. The species which extend furthest from 

 this optimum region are herbaceous forms. 



"4. The bog societies are normally related to the conifer forests in their 

 development to a climax tree vegetation. 



" 5. Where surrounded by oaks and hickories, or in general when conifers 

 are absent, they show no order of succession to the forest societies. This is 

 to be explained on the basis of the migrations forced upon all boreal societies 

 during glacial times. 



"6. The absence of conifers in the Ohio basin probably indicates the domi- 

 nance of broad-leaved forms there during glacial times. 



"Local lake and bog studies seem to indicate that: 



"1. Present bog habitats are continuations of similar habitats which existed 

 in early postglacial times, when tundra conditions and tundra vegetation 

 were dominant. 



"2. The temperature phenomena of undrained depressions, containing 

 deposits of peat, are favorable to the preservation of these types. 



"3. The 'drained swamp' and 'undrained swamp' classification will not 

 hold over any great area. Undrained and drained depressions are both favor- 

 able to the development of the common swamp plants. 



"4. The bog societies are composed of boreal species and, insofar as the 

 area of Ohio, Indiana, and southern Michigan is concerned, must be considered 

 as relicts of former chmatic conditions. The swamp societies, made up of 

 more southerly forms, must be considered as the normal hydrophytic vegeta- 

 tion of the present climatic conditions." 



Burns (1904 : 76) has described the successional zonation which occurs about 

 Dead Lake in Michigan. The zones from the center to the outside are as 

 follows: 



1. Nuphar, with Peltandra, Braaenia, and Utricularia. 



2. Sedges, largely Carex filiformis, growing in as high as 65 feet of very loose peat. 



3. Cassandra and other shrubs. 



4. Larix, Rhus, growing in peat 10 to 35 feet deep. 



5. Ulmus, Acer, growing in 5 to 10 feet of solid peat. 



6. Querais, Hicoria, on high gravel bank. 



Coulter (1904 : 39) has made a comparison of the general relations of pond 

 and swamp communities in the Middle West: 



