A Comparison Of Earlywood and Latewood Tracheid Lengths of Loblolly Pine

Literature reports on the relationship of earlywood and latewood tracheid length within individual growth rings of pine trees are contradictory and confusing. Latewood tracheids have been reported to be longer or shorter than, and the same length as, earlywood tracheids. This study compares earlywood and latewood tracheids of both juvenile and mature wood of trees in a loblolly pine plantation (phase 1) and reports tracheid length variation from first-formed earlywood to last-formed latewood at several sampling locations of one tree (phase 2).For the plantation-grown trees, earlywood and latewood were compared for ring 5 (juvenile wood) and ring 15 (mature wood) of 18 trees. In juvenile wood, first-formed earlywood cells were shorter than either last-formed earlywood or latewood tracheids. There was, however, little difference between last-formed earlywood and latewood. In mature wood, first-formed earlywood and last-formed latewood tracheids were the same average length. However, both earlywood and latewood tracheids formed near the transition zone were slightly longer.Measurement of tracheids, obtained by macerating serial microtome sections taken from earlywood to latewood of individual rings (phase 2), revealed large variations of tracheid length within rings. In some rings, tracheid length increased from earlywood to latewood, in others it decreased, and in others it was unchanged.The conclusion is that tracheid length is neither consistently longer nor shorter in the latewood portion of loblolly pine growth rings.