Structure and function of flexure wood in Abies fraseri.

Wood produced during flexure in one-year-old leaders of Abies fraseri (Pursh) Poir. (Fraser fir) was analyzed anatomically and radio-densitometrically. More xylem cells were produced in stems subjected to flexing than in stems that were not flexed. The lumens of tracheids produced in response to flexure were smaller than the lumens of tracheids in normal wood. This was manifest as an increase in the cell wall area/cell lumen area ratio. Microfibril orientation in flexure-induced wood approached the less extreme values found in compression wood. The growth ring composed of flexure-induced wood also had a greater density than normal wood. Compression wood, as defined by cellular characteristics observed in transverse section, was absent in flexed stems. Detailed analysis of the anatomical structure, wood density and biomechanical properties of flexure-induced wood indicated that it has more in common with compression wood than with normal wood.