220 Dr James Hector on the Physical Features of the 
Month. Air, Poplar. Spruce. 
1857. December, : ; 8°9 9°67 13°63 
1858. January, . ; 0-0 0° 0°8 
February, : 74 711 3°96 
Marohy jit a 26:3 29°27 20:93 — 
April, . : 35 8 35°54 oe 
So long as the vegetation remains dormant during the win- 
ter season, the sudden changes which have been described, 
however great, can have little influence upon plant life; but 
when the mean temperature for the twenty-four hours rises 
above the freezing-point, and the powerful sun of each day, 
with the abundant moisture derived from the melting of the 
snows, stimulate the ascent of the sap and the germination of 
seeds, these sudden alternations must have a very baneful 
effect, and exclude from the flora of the country many plants 
that it would otherwise be quite fitted to sustain. From the 
middle of March until the third week of April is the usual 
duration of this critical period; but as late as the middle of 
May serious damage is frequently done to the vegetation by 
sudden variations of the temperature. This is without taking 
into consideration the night frosts, which are of common oc- 
currence almost throughout the entire summer, and which, of 
course, must completely prevent the growth of many kinds of 
plants. 
During the summer months, even in the true prairie coun- 
try, rain, with cloudy weather, is much more frequent than 
might be expected from the position which the district occu- 
pies in the centre of a continent, and barred from the influence 
of the moist south-west winds by a continuous chain of moun- 
tains. On the prairies immediately to the west of the Red 
River settlement, as far as Turtle Mount, thunder-storms, with 
heavy rains, are of almost daily occurrence during the months 
of July and August. The temperature in that district was 
often very high, the thermometer several times reaching 95° 
in the shade. 
On the higher plains to the west, between Carlton and the 
Rocky Mountains, which range in altitude from 2000 to 
