,TM. 1-414
2 ARMY AIR FORCE
CHARACTERISTICS OF WOOD
Paragraph
T r e e structure__________________________________________ 2
Classification____________________________________________ 3
Cellular structure_________________________________________ 4
Medullary rays___________________________________________ 5
Springwood and summerwood ______________________________ 6
Grain___________________________________________________ 7
Common defects in wood___________________________________ 8
Factors affecting strength___________________________________ 9
2. Tree structure.--a. Examination of the cross section of a log
(fig. 1) discloses four distinct regions or sections: the bark, the sap-wood (light-colored layer next to the bark), the heartwood (darker wood inside the sapwood), and the pith (small, soft core of the tree).
As a general rule, the sapwood is lighter in color than the heartwood. However, in spruce, basswood, and others, there is very little if any