26 BOTANICAL GAZETTE [JULY 
constitute a large part of the shrub formation. Together with 
Decodon, it is found frequently indiscriminately mixed with facies 
in the central zone. In fact, the differences in the formation 
are to be seen largely in the ratios between the numbers of indi- 
viduals present, and not in their entire absence from either. 
THE MAPLE-ALDER ZONE 
With the maturity of the facies, a gradual change in the envi- 
ronmental conditions for the plants takes place. The annual leaf- 
fall covers the substratum with a visibly thicker layer of vegetable 
material rich in organic matter, and is followed by the growth of 
fungi and bacterial organisms favorable to succeeding plants 
through the formation of available nitrogen. Like snow and 
ice, the covering of fallen foliage reduces the extremes of soil 
temperature, suppresses the growth of Sphagnum, Oxycoccus, 
and similar plants from the adjoining central zone, and improves 
the production of a kind of humus of great significance to the 
animal life as well. Moles, earthworms, snails, and insects are 
not uncommon in this zone. The shade of the trees during summer 
and autumn checks extremes in evaporation, and thus reduces 
the transpiration from the herbs and shrubs beneath the trees. 
Through the combined action of these and various other agents, 
there is a corresponding rearrangement of some species and the 
disappearance of others. In places along the margin, the peat 
substratum is firmer, fairly well above the level of the lake, and 
comparatively better drained. These conditions are sufficiently 
established at the southeast side of the island to be characterized 
as the maple-alder zone. The bog tree formation is quite promi- 
nent, and though not extensive, it is still a strongly marked zone. 
The most conspicuous plants are large-sized maples (Acer rubrum), 
alders (Alnus incana, A. rugosa, Ilex verticillata), the chokeberry 
(Prunus melanocarpa), black cherry (Prunus serotina), and poison 
sumach (Rhus Vernix). Oaks (Quercus palustris, Q. imbricaria), 
ashes (Fraxinus nigra), and the silver maple (Acer saccharinum) 
are still relatively rare. The trees are surface-rooted. The roots 
do not penetrate to a depth of more than one foot (30 cm.). They 
spread out in all directions from the trunk, and are of sufficient 
