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From the foregoing we find that the peculiar features of temperature 
in Colorado are great extremes, great range, and sudden changes. 
Upon trees the effect of great extremes is not necessarily injurious, 
except in connection with a dry, porous soil, which, holding no moisture 
to form an icy protection, allows the frost penetrate so deep as to 
reach the tender rootlets of a young tree. Frost has been found in the 
ground in Colorado 5 feet below the surface. The evil effects of this 
may be lessened by heaping snow around the foot of the tree, where it 
will melt and freeze and protect the ground. When snow can not be 
had watermay beused. Late fall irrigation, just before freezing weather 
sets in, is therefore beneficial, from the coating of ice formed near the 
surface. Winter irrigation should also be practiced for thesame reason. 
The great range of temperature in Colorado is more injurious to trees 
than extreme cold, for all vegetation thrives best in equable climates. 
In winter the pow ail heat of the midday sun in this thin air excites 
the flow of sap in a tree to such an extent that it does not recover its 
normal condition before it is frozen by the severe cold of the night. 
Trees are found injured on the south, but never on the north, side. To 
remedy this, the trunk is shaded by a board, or wrapped with matting, 
burlap, or straw. More trees perish during the warm, summer-like days 
ef February than in the coldest weather. This great difference of tem- 
perature in sun and shade has also an unfavorable effect on trees in 
summer, retarding their growth and preventing the warm nights so 
beneficial to all vegetation. 
It is a well-known fact that sudden thawing is more injurious to plants 
than freezing, aud therefore the effects of cold are increased tenfold 
when followed by great warmth. For this reason sudden changes of 
temperature are the hardest for trees to endure. The hot blasts which 
come down from the mountains during severe cold often scorch the life 
from the tree, and the fierce blizzard from the north, which may sud- 
denly appear on the warmest day in winter, chills it 6 the marrow. 
We find little spring weather in Colorado, and the approach of sum- 
mer is not gradual, as at lower elevations. Trees will be often tempted 
to open their buds in the warm sunshine of many days in March and 
April, only to be nipped by late frosts. For this reason fruits are diffi- 
cult to raise, especially the early blossoming varieties. 
On account of this peculiar winter weather, trees planted in autumn 
suffer more than those planted in spring, which have the benefit of a 
whole season to become accustomed to the new and peculiar conditions. 
Those trees succeed best here which form their terminal buds early in 
autumn, and make a definite annual growth, so that their tops may not | 
be killed in the first frosts. 
HUMIDITY. 
Humidity, or the amount of moisture in the air, is a more powerful 
agency in climate than is generally recognized. It regulates light and | 
