The distribution and fine structure of the epicuticular leaf wax of Pseudotsuga menziezii

Observations were made by scanning and transmission electron microscopy on the distribution and fine structure of epicuticular wax crystals on the hypostomatic needles of Douglas fir (Pseudotsuga menziezii (Mirb.) Franco.). The wax crystals were aggregated in tufts of variable area and density in discontinuous but uniform distribution along the adaxial surface, abaxial midrib, and stomatal regions. The stomatal region showed the greatest density of wax crystals, filling the stomatal antechambers formed by subsidiary cells. Wax crystals were present on the abaxial margins in a gradient of density from that of the abaxial stomatal region to that of the adaxial surface. The epicuticular wax crystals on Douglas-fir needles are of open tubular form exclusively, with a mean outer diameter of 136 ± 12 nm, wall thickness of about 35–40 nm, and average length of 2.3 μm. In view of the helical striae observed on the outer crystal surface, an interpretation of possible substructure is discussed.