444 BOTANICAL GAZETTE [DECEMBER 
mara, Impatiens biflora, Eupatorium perfoliatum, Calamagrostis 
canadensis, Dryopteris thelypteris, D. spinulosa intermedia, Doel- 
lingeria umbellata, Lactuca spicata, Coptis trifolia, Boehmeria cylin- 
drica, Onoclea sensibilis, Marchantia polymorpha, and Rosa Carolina. 
The further development of these societies under present condi- 
tions will bring about a complete change. There can be no doubt 
that the poplars and red maples are the coming trees, with elm a 
close third. When these have become sufficiently large and numer- 
ous to overshade the shrubs, the latter will bé killed out, and we 
shall have in their place the maple-elm forest common to the low 
grounds. The shrubs, however, are capable of persisting for a great 
length of time, because of the difficulty of tree seedlings obtaining a 
start beneath them. 
THE CHELSEA BOG. 
Of the bogs which have been subjected to clearing, burning, and 
ditching, by far the most interesting in this region is located just to 
the southeast of the town of Chelsea. It covers an area of about 
50 acres (20 hectares), and the peat is reported to be 40 feet (12™) 
thick at the deepest places. The divisions into societies, as indicated 
on the map (fig. rz), are based on the most general characters of the 
vegetation. There are gradations between all of the societies, and 
these are so gradual that it is difficult to determine definitely the 
boundaries. Further, owing to the tendency of many of the shrub 
species to form dense local growths by the development of stems 
from underground shoots, the smaller associations are very diverse 
in different parts of the same society. 
Birch-vaccinium society.—This mixed society of bog shrubs occupies 
about one-fourth the area of the bog. Its substratum consists of 
peat standing about a foot above the average water level. The 
dominant plants are Betula pumila, Vaccinium corymbosum, Rubus 
frondosus, Aronia nigra, Vaccinium canadense, and Pteridium 
aquilinum. Just as common perhaps, but of lower growth, are 
Rubus hispidus, Spiraea salicifolia, S. tomentosa, Aralia hispida, 
Chamaedaphne calyculata, and Rumex Acetosella. The ground 
covering, except beneath the dense shade of the shrubs, is made up 
of Polytrichum juniperinum. There are many small areas of which 
this plant now holds exclusive control, and forms a rich carpet of 
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