TREES 



365 



lows and birches, extend far northward. Mahogany, teak, 

 and the palms flourish only in the tropics. Oranges and 

 lemons thrive in California, but not in Minnesota. Each 

 species has a certain range to which it is limited principally 

 by the climate. On the borders of these ranges the trees do 

 not thrive so well. In high altitudes, or far northern lati- 



FiG. 156. Cottonwoods, Soft Maples, Boxelders, Elms, and Willows Like to Grow 

 Along the Rivers. Their Seeds are Carried by Wind and Water. 



tudes, the trees are stunted in their growth, and finally a 

 limit is reached beyond which trees do not grow the tree 

 line. 



Moisture is probably the next most potent condition de- 

 termining the distribution of trees. Some trees, like the 

 cypress of the southern swamps and our northern tamaracks, 

 can grow only where they can stand with their feet in the 

 water or water-soaked soil. In northern Minnesota one may 



