CHAPTER III 



THE LIFE PROCESSES OF TREES AND THE NATURAL 

 FACTORS THAT INFLUENCE THE LIFE OF TREES 



Since a tree is a living organism it must carry on certain 

 life processes. It must breathe, absorb and digest food, and 

 transport nourishment to the parts needing it. Many of the 

 life processes in trees are similar in kind to those in animals. 



Breathing or Respiration. — Breathing takes place through 

 minute openings usually on the under side of leaves called 

 stomata. The tree breathes in oxygen and breathes out car- 

 bonic acid gas the same as an animal. The oxygen is used in 

 carrying on the life processes of the tree. To some extent, 

 especially in the winter after the leaves have fallen, breathing 

 takes place through small openings or lenticles in the bark of 

 the trunk, branches or roots, the oxygen being conducted to 

 the inner portions of the tree along the medullary or pith 

 rays. 



Absorption and Transpiration. — The food of trees is ab- 

 sorbed through the root hairs and through the leaves. The 

 food absorbed by the root hairs is water and dissolved mineral 

 salts, that absorbed by the leaves is carbonic acid gas from the 

 air. The water and mineral salts are carried up through the 

 new wood to the leaves. The salts are contained in the 

 ground in very weak solutions. In order that enough may be 

 brought up to supply the needs of a tree, a far greater amount 

 of water must be absorbed than is actually needed. The ex- 

 cess of water passes out through the stomata of the leaves as 

 water vapor. 



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