488 BOTANICAL GAZETTE [DECEMBER 
black spruces grow everywhere on the low swampy grounds. South 
of the Ottawa River it grows principally on low and level land.” 
Low states, ‘‘ Larix is probably the hardiest tree of the subarctic 
forest belt. Throughout the interior it is found in all the cold 
swamps and is always the largest tree in the vicinity. Along the 
northern margin of the forest the larch continues a tree to the very 
edge where the black spruce is dwarfed to a mere shrub. Larix 
demonstrates the principle that a tree which has a wide range of 
tolerance does not flourish in competition with species of smaller 
range, but is crowded into situations where conditions exclude 
competitors. Such a form is usually of slow growth compared with 
forms which are more specialized. Larix cannot be called a 
xerophyte, a hydrophyte, or a mesophyte, since it may be any of 
the three. Although it is usually found under extreme conditions, 
it grows best under mean conditions, provided competitors have 
been eliminated. The distribution of Larix is accounted for by 
its wide range of tolerance, together with its low status in the com- 
petition scale.” 
THUJA OCCIDENTALIS.—The “anomalous” distribution of Thuja 
occidentalis defies explanation by regarding temperature, water, 
or soil as the limiting factors (figs. 1, 2). ‘It is absent in New- 
foundland, Cape Breton, Nova Scotia, and the east half of Prince 
Edward Island, but unusually large and fine in New Brunswick and 
the Gaspé peninsula, in which the climate, soil, etc., are the same 
as in the adjacent regions, where no trace of the species is to be 
found.”” Bett (2) also states that ‘there is a remarkable outlier 
of white cedar brushwood around Cedar Lake on the upper part of 
the Saskatchewan River at a distance of 190 miles to the north- 
west of the nearest point of the main area covered by this species.” 
Moreover, it is notable that throughout great areas, for instance the 
Temagami region, Thuja is unknown, while in the surrounding 
country it is abundant. T. occidentalis has a wide range of toler- 
ance toward environmental conditions. The presence of out- 
liers’’ where conditions are similar to those prevailing in other 
regions where it ordinarily occurs indicates that the general 
area of its distribution does not extend to its ecological limit, in 
many instances at least. The northern area of its distribution is 
