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18.25, at Chicago 37.34, and at New York 43.58 inclies. The general 

 . distribution of rain-fall in this region is shown by the table, which gives 

 the amounts for each month and season. In Colorado winter is the dry 

 season and summer is the wet season j the driest months are January 

 and February, and the rainiest are May and J-uly. This is due to the 

 altitude and inland position, for we find just the reverse at Los Ange- 

 les, where 10.43 inches, more than half the annual rain-fall there, falls in 

 winter, and only 0.22 inches in summer. At New York the rain-fall is 

 very evenly distributed throughout the year. A fact, not evident 

 from the table, is that no rain falls, as a rule, in Colorado, between 

 October and April. The storms that gather then are accompanied by 

 such cold as to precipitate only snow, which is quickly melted and ab- 

 sorbed or evaporated. The heaviest fall of snow during the last ten 

 years, about 2 feet deep, totally disappeared within a week. The large 

 snow storms invariably come from the southeast, though a whirl of 

 snow is generally driven before the fierce northers. This snow-fall 

 being small and quickly disappearing in the warm sun and dry air, 

 it has no opportunity to exert upon the air its cooling influence by 

 increasing radiation and by hindering the warming of the ground. 



The winter weather, as we have already found, extends into April 

 and even May, and ends with a heavy snow or rain storm, lasting two or 

 three days. Settled warm weather may then be depended on, but not 

 before. The wet season begins generally about the first of July and re- 

 mains six or eight weeks. During this season almost every day will 

 bring its shower, which, coming in the afternoon, passes over before 

 night, leaving the evening cool, fresh, and beautiful, or it will clear 

 during the night, bringing most delicious mornings, with a wonderful 

 clearness of atmosphere. The summer ends as it began, with a heavy 

 rain-storm, late in August or early in September. This latter month is 

 generally more or less rainy, but October and November bring the per- 

 fection of autumn weather, extending often to Christmas. 



With so little of their chief means of support, it is not to be wondered 

 at that the only trees growing spontaneously in Colorado are the narrow 

 belts of Cottonwood that mark the course of the streams on the plains, 

 and the groups of hardy Pines, Spruces, and Firs on the northern slopes 

 of the mountains, or in the sheltered canyons. When these are de- 

 stroyed nature finds it hard to renew the growth in any way, and only 

 succeeds in the more favored localities. It may be accepted as a general 

 truth that on these plains, and in many parts of the mountains, in most 

 situations no tree can be expected to grow by the natural rain-fall. Irri- 

 gation is therefore a necessity, and as a system it has been brought to a 

 high state of perfection during the past twenty years. 



Water must be supplied to trees, not only in their growing season, 

 but also during the dry winter months to aid in the small circulation of 

 sap required to keep life in the tree during its long sleep, and to com- 

 pensate for the evaporation from its bark. The tree needs much water 



