446 BOTANICAL GAZETTE [DECEMBER 
the Polytrichum is killed out by the shade. Rumex Acetosella is 
better fitted to withstand such conditions, and consequently forms 
an inner border about each group of shrubs. Where depressions 
occur and are flooded for any length of time, the Polytrichum is 
replaced by Eriophorum virginicum and Scirpus cyperinus. Along 
the northwestern border Rubus nigrobaccus is making inroads upon 
this society. To the north of the railroad, however, the most impor- 
tant changes are being wrought by the development of Populus 
tremuloides and Quercus velutina. Young trees of the former are 
now scattered throughout, while the latter is present in small number. 
The plants of minor importance are Ilex verticillata, Viburnum len- 
tago, Ilicioides mucronata, Amelanchier Botryapium, Euthamia 
graminifolia, Doellingeria umbellata, Bidens trichosperma tenuiloba, 
Dulichium arundinaceum, Poa flava, and Sphagnum cymbifolium. 
Chokeberry society.—Aronia nigra forms the most dense and 
exclusive growth that occurs on the bog. Usually the substratum 
is somewhat lower and more subject to overflow than in the last — 
society. It would seem from observation that this condition is in 
part due to the chokeberry itself. Owing to its dense growth, it 
protects the surface of the peat from drought and favors the processes 
of decay. At the same time it adds very little to the substratum in 
the way of débris. Where it attains its best development it is prac- 
tically without undergrowth. About the borders it is mixed with 
Vaccinium corymbosum, Betula pumila, and Ilex verticillata. Of 
the smaller plants, Pteridium aquilinum penetrates to the greatest 
distance. Other species occurring about the borders are mentioned 
among the other societies. 
Poplar-willow society.—About the borders of the bog, and extend- 
ing to a greater or less extent into its interior, is a dense zone composed 
of Populus tremuloides, Salix discolor, Quercus velutina, Populus 
grandidentata, and Salix nigra. By far the most abundant form 1s 
the trembling aspen. The substratum varies from areas well above 
the water level to areas which are constantly submerged. The aspen 
is also the most important of the plants which are invading the shrub 
societies. In the relative proportion of the individual species there 
is the greatest variation at different places in this border zone. O 
the more enduring species, Quercus velutina is the most abundant. 
The other species present are Salix Bebbiana, S. sericea, S. lucida, 
