150 
Heartwood and sapwood. The wood of large tree trunks 
A TEXTBOOK OF GENERAL BOTANY 

consists of an outer region known as sapwood and an inner 
portion, the heartwood. ‘The sapwood is usually light in color 
and from about a centimeter to several centimeters in thickness. 
In the sapwood the parenchyma cells are alive, and so it is in 
this portion of the wood that food is stored. Also, the ascending 

















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Fig. 147. Tangential section of wood of 
Erythrina fusca 
A vessel is in the center, wood fibers with thick 
walls and pointed ends are at the sides, and 
the elongated, blunt-ended cells are wood 
parenchyma. The groups of cells containing 
starch grains are pith rays. (x 75) 
current of water moves 
in the sapwood, and not 
in the heartwood, which 
has practically no other 
function than that of 
mechanical support. The 
heartwood frequently has 
a darker color and is more 
resistant to decay than is 
the sapwood. Wood does 
not decay by itself, decay 
being due to the action of 
bacteria and fungi. The 
parenchyma cells of the 
heartwood are generally 
dead, but before they die 
they usually produce tan-, 
nin, or some other an- 
tiseptic material, which 
permeates the walls of the 
neighboring cells. This 
antiseptic material makes the wood more resistant to the attacks 
of bacteria and fungi, and it is for this reason, and also because 
the heartwood contains less food material than the sapwood, 
that the heartwood is generally more resistant to decay and to 
the attacks of insects than is the sapwood. The dark color of the 
heartwood is also usually due to tannin, resins, or gums pro- 
duced by the parenchyma cells. 
Weight of wood. The variation in weight of woods is very 
ereat, as they contain varying quantities of air, but the wood 

