• Schwarzmann, Joseph M.
  University of Maine Graduate School
  

This study was made to determine the anatomical sequence of lignification in normal wood of balsam fir, Abies Balsamea (L.) Mill. Transmission electron microscopy was used to study the sequence. The potassium permanganate fixed samples used were taken throughout an entire growth season from one tree.

In trahceids, lignification was found to be initiated in the middle lamella between pit borders of adjacent tracheids. Lignification then extended almost immediately into the initial pit border and cell corners. In cell corners, lignification was initiated in the outer portion of the primary wall or the middle lamella. Lignification then proceeded into the S1 layer of the secondary wall in the cell corners leaving the major portion of the primary wall unlignified. Lignification first proceeded along the tangential wall farthest from the cambium, after lignification had begun in all cell corners. Then lignification spread along the radial walls and finally along the tangential wall closest to the cambium.