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. Aguatic sociEry. Potamogeton natans, P. lucens, Nym- 
phaea advena, Castalia odorata. 
2. Cat-rart-Duticuium 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. 
