28 FARM FORESTRY 



a tree grows well in bottomlands or along streams is no reason 

 to believe that it will thrive when planted on a ridge, even if 

 the composition of the soil is the same. 



Food. Trees as well as other forms of organic life de- 

 mand food for carrying on their life functions. As we have 

 already learned trees absorb food through their leaves and 

 through their roots. They obtain a large portion of their 

 food from the air in the form of carbonic acid gas, the supply 

 of which is sufficient for all trees. They obtain mineral salts 

 and water from the soil through their smaller roots. The de- 

 mand made by trees on the soil varies with different species. 

 Some trees will grow on an almost sterile, sandy soil, while 

 others demand as rich and fertile a soil as do agricultural 

 crops. Pitch pine will grow on thin, dry soil on the tops of 

 ridges, while black walnut and catalpa demand the best of 

 soil conditions for good growth. 



