three components, the wood or xy/em which car- 
ries the water and soil salts up to the leaves, and 
the phloem which carries the manufactured food 
and water down to the stems and roots to provide 
energy for life and growth. In older trees a cam- 
bium develops between the xylem and phloem. 
This is an embryonic tissue which through divi- 
sion and differentiation of its cells adds internally 
to the xy/em and externally to the ph/oem tissues. 
THE ROOTS 
The function of the roots—other than anchor- 
ing the tree—is to absorb water and dissolved 
salts (nitrates, phosphates and sulphates) from 
the soil. To better accomplish this the absorbing 
surface of the root is increased many fold by 
many small root hairs. The root grows (by a 
division and differentiation of cells) toward the 
center of gravity and to sources of water and 
solubes. Since nearly all natural soils (that 1s, 
soils not depleted of salts by successive planta- 
tions and removals of dead plant material) have 
the required mineral salts and since all soils but 
those in arid regions have moisture, the great 
root surfaces absorb quantities of water which 
contains these salts in solution. This solution 
enters the conductive cells in the xy/em of the 
roots and is carried upward through the stem to 
the leaves. 
THE STEM 
The stem is composed of xylem and phloem, 
the bark or cork which is waterproof to prevent 
the evaporation of the water from the tissues, 
and a layer of cells called the cambium lying 
between the xy/em and phloem, and which in the 
spring and summer produces new cells to increase 
the size of the roots, trunk, and branches of the 
tree. Between the vascular bundles are relatively 
3 
