64 Rhodora [Marcu 
trees were taken which showed trunks at each locality of about fifteen 
feet in cireumference."! 
These facts indicate conclusively enough that, although in swamps 
Thuja forms impenetrable tangles of low, usually interlocking, small 
trees, it is on the better-drained or even xerophytic rock-habitats 
that it develops its full stature. Consequently if, as Hutchinson says, 
water is the “limiting factor” which prevents Pinus Banksiana from 
spreading into the limestone region southwest of James Bay, it cer- 
tainly cannot be argued that lack of water is the factor which keeps 
Thuja from pushing north on the acid Archaean country; but, even 
if it be urged that Thuja most commonly occurs in swamps, it must 
be evident that there are plenty of swamps on the Labrador Peninsula, 
for Low tells us that water covers “at a moderate estimate, at least 
one fourth of the total area” of the peninsula (Low, n. s. viii. 23L). 
Hutchinson (p. 488) says, further, that “The presence of ‘outliers’ 
. 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 roughly outlined by a semicircle, a fact which 
contributes evidence that Thuja has migrated radiately from a limited 
area . . . it does not migrate rapidly . . . this form has lagged behind." 
When, therefore, following Hutchinson’s suggestion, we draw the 
circle connecting the “outliers” (in western North Carolina, western 
Prince Edward Island, western Anticosti, and Cedar Lake on the 
Saskatchewan) it is impressive to find that the center of the circle 
falls in the great acid Archaean area northeast of Lake Superior, the 
Temagami region; for Hutchinson particularly informs us that “it 
is notable that throughout great areas, for instance the Temagami 
region, Thuja is unknown." And since the Temagami region was 
not accessible to forests until after the vanishing of the Pleistocene ice, 
by Hutchinson’s interpretation that the tree has “migrated radiately ” 
we are forced to the dramatic picture of the infant Thuja occidentalis 
created in very modern times in the center of the Temagami region 
and finding nothing to live on, migrating as rapidly as its "lagging" 
tendency would allow to the calcareous regions northwest, north, 
east, and south! 
Wherever the “Cedar swamp” is open and full of glades or swales 
it supports a characteristic vegetation quite unlike that of the acid 
1 Small & Vail, Mem. Torr. Bot. Cl. iv. 167 (1893). 
