226 



From the foregoing we find that the peculiar features of temperature 

 in Colorado are greaft 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 nomoisture 

 to form an icy protection, allows the frost to 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 water may be used. Late fall irrigation,jast before freezing weather 

 sets in, is therefore beneficial, from the coating of ice formed near the 

 surface. Winter irrigation should also be practiced for the same 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 powerful 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 

 of 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, and 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 to 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 



