366 NATURE-STUDY 



ride fifty miles or more through pure tamarack swamps. 

 The soft maple and the willows prefer wet soil, and hence 

 do best at the edges of streams, lakes, and sloughs. Elms 

 also like a rather moist soil, and grow very large in the bottom- 

 lands of rivers. But many trees can "endure a dryer soil. 

 The black oak and Jack pine will grow in very dry soil, but 

 there is a limit even for these. 



In a region where the annual rainfall is less than twenty 

 inches trees grow only with difficulty, or not at all. The 

 eastern half of the United States was originally forest covered. 

 But as we go west we gradually see that the Big Woods are 

 less luxurious and flourishing. The trees are smaller and 

 stand farther apart. On this dividing fine are straggling 

 scrub oaks and poplars, and these also eventually disappear. 

 In the valleys of streams and on the borders of lakes, there 

 still manage to exist on the prairies various species of hard 

 woods. 



The principal reason for the treeless condition of the prai- 

 ries is lack of rain. It is only under artificial culture 

 that the young trees can become established. Once well 

 rooted they manage to grow, though not as large as in better 

 watered regions. 



A visit to a forest will teach us much about the life of the 

 individual trees, and the forest as a community of trees. 

 In our northern or central wooded regions we find generally 

 a mixed stand of hard woods, such as elms, oaks, maples, 

 ironwood, hickory, butternut, poplar, etc. The trees are 

 of all ages, from germinating seedlings to patriarchs cen- 

 turies old. There are mature trees with leafy crowns 50 

 to 100 feet high, that have won in the struggle for fight. 

 There are younger trees in the shade of the older. Young 



