THE NORTH TEMPERATE ZONE 87 



the foliage of the deciduous trees seems to expand almost over 

 night. Where the deciduous forest prevails, the spring is marked 

 by a profusion of delicate herbaceous perennials, such as violets, 

 spring-beauty, blood-root, anemones, etc., which spring up very 

 quickly and flower before the leaves of the trees expand. They 

 soon mature their fruit, and in a few weeks have mostly disap- 

 peared, remaining dormant until the next spring. 



A feature of these deciduous forests is the magnificent display 

 in the autumn when the varied species show a wonderful variety 

 of brilliant colors in the ripening foliage. The gorgeous dyes of 

 the sugar and scarlet maples; the crimson, purple and scarlet of 

 the gums; the gold, russet and wine reds of the oaks, hickories, 

 dogwoods and ash, and the blood-red sumacs, huckleberries, and 

 many other shrubs, combine to make an unrivalled display of 

 splendid color. 



While temperature is a very important factor in plant distri- 

 bution, moisture is perhaps even more so. The whole eastern 

 United States is a well watered country, abundantly blessed with 

 great rivers and lakes, and consequently having an ample rainfall. 

 The precipitation is heaviest in the southern coastal regions and 

 the slopes of the southern mountains; but throughout the region 

 east of the Mississippi there is a rainfall of 30-60 inches, and 

 nearly the whole country was covered originally with heavy 

 forest. 



Westward the precipitation falls off materially, and this com- 

 bined with a much higher evaporation, results in conditions un- 

 favorable for tree growth ; and these conditions become still more 

 marked in the elevated plains adjacent to the Rocky Mountains. 

 In the cooler northern regions of Montana and Western Canada, 

 the prairie reaches to the foot of the mountains; further south the 

 western plains are arid, and may be described as steppes, rather 

 than true prairie. 



The absence of any mountains between the Rockies and the 

 Appalachians, exposes all of the eastern United States to the great 

 air movements originating in the Canadian Northwest. The 

 effect of the "cold waves," starting in the far northwest, are felt 

 as far south as the Gulf States. 



Topography plays a minor role in the climate of eastern North 

 America, the two most important factors being latitude, and 



