1922] WATERMAN—PLANT COMMUNITIES 15 
growth grows on the peaty soil which has collected in hummocks 
or on the layer of tree roots. Shade-tolerant mosses are abundant, 
and occasional restricted patches of sphagnum occur. Among 
flowering plants the most common are Coptis trifolia, Cornus cana- 
densis, Trientalis americana, Maianthemum canadense, Aralia nudi- 
caulis,Gaultheria procumbens, Viola spp., and occasionally Clintonia 
borealis. Aspidium spinulosum and Osmunda regalis are frequently 
found, and some Taxus canadensis. 
Fic. 7.—Algonquin shore, kept steep by erosion of Otter Creek 
VEGETATION OF RIVER AND LAKE BORDERS.—In the Platte Plains 
there are no true alluvial floodplains, and the shores of streams and 
bodies of water are either rather steep sandy slopes, or else shallow 
bays or lagoons inhabited by one of the types of communities already 
described (figs. 6, 12).. The lakes are frequently shallow some dis- 
tance from shore, and these shallows generally contain extensive 
colonies of Scirpus. There is usually a fringe of aquatic plants, 
including Typha latifolia, Sparganium, Sagittaria, Scirpus, etc., or of 
shrubs including Myrica Gale and Decodon verticillatus. On flowing 
Streams the latter does not seem to advance from year to year, 
Probably on account of being torn away by ice in the spring. In 
