1903] BOG PLANT SOCIETIES 403 



"undrained" types of swamps occurring in the area of lakes and 

 sand dunes at the southern end of Lake Michigan. Although 

 several species of plants may be common to two or more, he does 

 not believe these societies to be related to one another genetically. 

 That a certain amount of chance in the matter of seed dis- 

 persal must be taken into account in any botanical field problem 

 is recognized. But the fact that "drained" and "undrained" 

 swamps occur in close proximity to one another, each with numer- 

 ous examples in the same district, seems to require some more 

 adequate explanation. 



RELATION TO SURROUNDING VEGETATION. 



Throughout the region of northern Indiana, northern Ohio, 

 and southern Michigan the problem is still further complicated 

 by a seeming absence of all connection between the bog societies 

 and the bordering forests. The zonal succession of plant groups, 

 from the submerged aquatics of the pond to the arborescent 

 forms of the higher bog margin, are clearly defined and well 

 known. But then comes a sudden break, and without a sugges- 

 tion of gradation the surrounding forest of mature oaks or oaks 

 and hickories appears. 



Farther north in Michigan there is no such difficulty in finding a 

 definite order of succession between the bogs and forests sur- 

 rounding them. For example, a tamarack swamp on north 

 Manitou Island, which is surrounded by a thick forest of maple 

 and beech, shows the following societies arranged almost zonally, 

 beginning with the open pond in the center: 



1. AQUATIC SOCIETY. Potamogeton natans, P. lucens, Nym- 

 phaea advena, Castalia odorata. 



2. CAT-TAIL-DULICHIUM SOCIETY. Typha latifolia, Phrag- 

 mites Phragmites, Menyanthes trifoliata, Dulichium arundina- 

 ceum, Cicuta bulbifera, Scheuchzeria palustris. 



3. CASSANDRA SOCIETY. Chamaedaphne calyculata, Dryop- 

 teris Thelypteris, Sphagnum sp. ?, Kalmia glauca, Sarracenia 

 purpurea, Ledum groenlandicum, Lycopus americanus, Tria- 

 denum virginicum, Polygonum Hydropiper, Rubus hispidus, 

 Comarum palustre, Andromeda Polifolia, Chiogenes hispidula, 

 Oxycoccus Oxycoccus, and Eriophorum virginicum. 



