4 MISC. PUBLICATION 162, U. S. DEPT. OF AGRICULTURE 
Air Supplies carbon. 
the principal food of 
the tree.laken in 
through the leaves. 
Tree increases each year in 
height and spread of branches 
by adding on mew growth of 
twigs 
Leaves prepare 
pieteed oben ; 
rom airand sai Light and heat 
and give off 2; = 
CROWN 
moisture by 
o> necessary for 
Transpiration - 
= 
Chemical changes 
if 2 
Heartwood (inactive) 
gives strength 
Sapwood carries sap 
TRUNK from root to leaves 
The .breath:ng pores of 
the entire tree=on leaves 
twigs: branches, tnuink and 
roots take 1n Oxygen. 
Flooding. poisonous gases. 
orsmoke may killa tree 
Cambium (microscopic) 
butlds the cells 
Inner bark carries 
prepared food from 
leaves to Cambium layer 
Outer bark protects 
tree from injuries 
Surface roots 
WZ ASNT 
Root tips orroor heirs take 
up water containing smal 
Quantity af minerals in 
Solution 
FIGURE 1.—How a tree grows. 
The buds, root tips, and cambium layer are the growing parts of the tree. Water 
containing a small quantity of minerals in solution is absorbed by the roots, 
carried up through the sapwood to the leaves and there combined with carbon 
from the air to make food. This food is carried by the inner bark to all 
growing parts of the tree, even down to the root tips. 
