194 CLIMAX FORMATIONS OP NORTH AMERICA. 



Pennington (1906 : 54) has described the following serai zones about Mud 

 Lake in Michigan: 



1. Marginal zone: (1) marBh-graes, (2) cat-tails, (3) wiUow, (4) poplar-ehn-osier 



societies. 



2. Tamarack zone: (1) tamarack, (2) tamarack-spruce, (3) AroniorVaccinium clear- 



ing, (4) tamarack-bum societies. 



3. CassandrchSphagnum zone, in which Vaednium, Gaylussacia, Larix, atad Picea are 



invading. 



4. Floating-mat zone: Carex, Dryopteris tkelypteris, Typha. 



5. Water-plant zone: Sdrpus lacustria, Pontederia cordata, Nymphaea advena. 



Transeau (1906) in studying the bogs of the Huron River, concludes that the 

 physical and chemical data now available fail to account for the differences in 

 the swamp flora of the region. The most important factor is believed to be 

 their physiographic history. The bog vegetation occupies undisturbed habi- 

 tats which date back to Pleistocene times. In habitats of recent origin or 

 recently disturbed is found swamp vegetation or a mixture of swamp and bog. 

 Experiments indicate that the bog-water itself has no tendency toward the 

 production of xerophilous modifications. Low soil temperatures and lack of 

 soil aeration, however, cause a reduction in the development of the several 

 plant organs. When these two factors are combined, the effect is very marked. 

 Experiments with Larix indicate that mycorrhiza develops only in poorly 

 aerated substrata and that the acidity of the substratum is not a factor in its 

 development : 



The successional zones are described for a number of lakes and swamps, 

 which show variations of the course of development. The following series 

 will serve to illustrate the hydrosere and its included oxysere: (1) aquatics, 

 Scirpvs lacustris, Castalia tid)erosa, Sagittaria rigida; (2) sedge-grass society, 

 Carex, Panicularia, Heleocharis, Dulichium, Dryopteris; (3) willow-maple 

 society, Salix, Cornus, Acer, TJlmus; (4) upland forest: (2) bog-sedge and shrub 

 society, Carex, Dryopteris, Menyanthes, Heleocharis, Typka, Salix, Betvla, 

 Oxycoccus, Andromeda; (3) tamarack society. 



Davis (1907) has made the first comprehensive study of the formation of peat 

 in America and its relation to succession. His treatment is divided into three 

 parts, namely: 



(1) ecology of peat formation in Michigan; (2) formation, character, and 

 distribution of peat bogs in the northern peninsija of Michigan; (3) economics 

 of peat. The successional relations of the various consocies and socies is 

 treated in such detail in part one that an adequate summary is impossible here. 

 The filling of depressions is considered at length (130), but the stages of the 

 general process are as follows: (1) zone of Chara and floating aquatics; (2) 

 zone of Potamogeton; (3) zone of water-lilies; (4) floating sedge-mat; (5) shrub 

 and Sphagnum zone; (6) zone of tamarack and spruce. 



The peat deposits are classified upon three bases, viz: (1) according to the 

 form of the land surface upon which they have been formed, (a) depressed 

 surfaces or hollows, (b) surfaces not hollowed out; (2) according to method of 

 development, (a) by successive generations of plants, starting from what is 

 now the bottom of the peat, (6) by growth at the sides, or at the top of the 

 basin, or both; (3) according to surface vegetation, as follows: 



(1) Elm and black ash swamps. (6) Heath (blueberry, cranberry, Cassan- 



(2) Tamarack swamps, marshes, and bogs. dra) swamps, marshes, or bogs. 



(3) Cedar (arbor vitae) swamps. (7) Grass and sedge marshes or bogs. 



(4) Spruce swamps. (8) Rush marshes (cat-tail and bulrush). 



(5) Willow and alder swamps. (9) Moss bogs (including Sphagnum bogs). 



