188 MINNESOTA STATE HORTICULTURAL SOCIETY. 
1,200 feet; when the air is deprived of its humidity, and dew a phenome- 
non from its rarity—all this taking place with an average temperature 
in summer of 66° to 75° during the day, with a fall at night as low as 40°. 
Fifth-—Another climatic influence in Minnesota and Dakota is the open 
nature of the region northward to Hudson Bay and the Arctic Circle: with 
no high mountain range to shield from the cold winds, or prevent the 
drenching rains of an atmosphere saturated with the chilling evaporation 
of vast bodies of cold water, which are only overcome and combatted by 
the dry warm westerly winds originating in the Rocky Mountains, with 
the winter climates that prevail occasionally from southern Colorado to 
the Arctic Circle. 
Sixth--The slightly modifying influence of latitude, coupled with de- 
creasing altitude as we go eastward to the Missouri and Red River valleys, 
an influence that exerts itself plainly in arboriculture, and seems to offer 
a barrier to their extension westward, although the thermometer appears 
fully as favorable as in lower altitudes elsewhere, where the same grow 
without impediment. 
The Rocky Mountain range from the 36° to 49° N. lat. has a westerly 
trend from the 105° W. long. in Colorado to the 115° W. long. at the Brit- 
ish American boundary. 
East and northeast of this range, the open, treeless expanse of the 
plains of the Missouri valley are in ‘ersected by a multitude of large 
rivers, and their affluents, whose main sources are in the Rocky Mountain 
snowfields, whose abundant supplies of icy water are finally precipitated 
into the Mexican gulf, surcharged with the abraded matter of our high 
mountains and table lands. 
This immense amount of precipitation is not derived from the Pacific, 
for the California, Oregon and Washington coast ranges cut off the Pacific 
Ocean humidity, while the humidity gathered in the Great Basin, and 
western Colorado is retained by the Wahsatch Mountains first, then by 
the Rocky Mountain range, thus arresting the moisture-laden clouds on 
their western slope. Hence our mountain supplies are obtained from the 
evaporation of this enormous treeless region, together with the evapora- 
tion of the Atlantic and Hudson Bay. 
The excessive dryness of the atmosphere over the region indicated is 
not very favorable to the culture of maize and sorghum, plants that require 
rain on their abundant leafage to come to their maximum perfection, 
which irrigation cannot supply. This condition rules likewise in Colo- 
rado, and is independent of the question of temperature, for in western 
Dakota, and even as far north as Helena, Montana, excellent corn is 
raised in Jefferson Park on the Missouri River without irrigation, when 
planted on the low bottom lands of that river; while the cactis, a more 
southern plant, has been found as far north as Winnipeg Lake. 
So we can safely say that the agriculture of the region extending from 
Red River to our Rocky Mountains, will be largely limited to herbaceous 
plants and under-shrubs, and to fruits that, in addition to their capacity 
to resist the high, dry temperature of our open plains in summer, must be 
fitted to withstand the excessively cold nights of a-continental climate, 
such as prevail in Minnesota, Dakota, Montana, Colorado, Wyoming, 
Idaho and Utah. 
