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 debris. 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 is 

 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. Of 

 the more enduring species, Quercus velutina is the most abundant. 

 The other species present are Salix Bebbiana, S. sericea, S. lucida, 



