Central Part of British North America. 227 
In treating of the distribution of plants in British North 
America, Sir John Richardson* has divided the region into 
three zones, in the following manner :— 
1. The Polar Zone, which embraces the land lying detached 
from the continent, and north of Lat. 73°. The flora of this 
zone consists of plants belonging to 21 natural orders, among 
which the Crucifere, Graminee, and Saxifragacee, are the 
principal. 
2. The Arctic Zone, which extends from the above-mentioned 
limit south to the Arctic Circle, excepting towards the eastern 
side of the continent, when, owing to the configuration of the 
land and the abnormal depression of the temperature, the 
characteristic Arctic flora passes for 10° south of that limit. 
An outlier from this flora also passes the south along the 
ridge of the Rocky Mountains. The number of natural fami- 
lies is in the Arctic Zone increased to 67, and the most marked 
feature is the predominance of Cyperacee. 
3. The Woodland Zone, which stretches across the conti- 
nent obliquely, conforming to the divergence of the Arctic Zone 
from its proper latitudes, and thus lying between 45° and 55° 
of latitude on the Atlantic coast, but between 50° and 60° of 
latitude on the Pacific coast. 
This zone he divides into three districts— 
1. The Eastern Woodland district of Canadian Forest, 
which extends westward as far as Lake Winipeg. 
2. The Western Woodland district, from the Pacific coast 
to the Rocky Mountains. 
3. The Central or Plain district, lying east of the Rocky 
Mountains. 
The number of natural orders represented in this zone is 
about 117, being an increase of 50 over the number in the 
Arctic Zone. 
As M. Bourgeau returned to England at the commence- 
ment of the third season’s explorations without crossing the 
Rocky Mountains, his collection only consisted of the plants 
gathered from between Lake Superior and the eastern slope 
of that range. It thus represents a portion of Richardson’s 
Eastern district, nearly the whole of the Prairie district that 
* Arctic Searching Expedition 1851, vol. ii, App. No. 3, 
