229 
18.25, at Chicago 37.34, and at New York 43.58 inches. 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; the driest months are January 
and February, and the rainiest are May and July. 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-fail 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 suow, 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. Thelarge 
snow storms invariably come from the soutbeast, thongh 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, latein August or early in September. This latter month is 
generally more or less rainy, but October and November bring the per- 
fection of antumn 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 courseof 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 
uth 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. Ivvi- 
ration is therefore a necessity, and as a system it has been brought toa 
high state of perfection during the past twenty years. 
Water must be supplied to trees, not only in their growing season, 
jut also during the dry winter months to aid in the small cireulation of 
ap required to keep life in the tree during its long sleep, and to com- 
ansate for the evaporation from its bark. The tree needs much water 





































