Variation with Tree Age of Needle Cuticle Topography and Stomatal Structure in Pinus radiate D. Don

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Abstract
Scanning electron microscopy reveals differences in the surface topography and stomatal structure of 1-year-old needles of Pinus radiata sampled from trees of different ages. The cuticular ridges on young-tree needles show an even pitch, whereas the ridges on mature-tree needles appear slightly puckered, with small discontinuities. The stomata on mature-tree needles have a smaller pore (10–15 μm) than young-tree needles (15–20 μm). In young trees a fine rodlet, or tubular wax covers the walls of the guard and subsidiary cells. The stomatal antechamber predominating in mature-tree needles contains an amorphous wax, which frequently closes the pore between the overarching stomatal lips. The yield of crude wax from chloroform extracts of needles of trees of all ages is approximately 0.2 per cent, and there is more of the acidic component in the wax of mature-tree needles. It is suggested that wax occlusions within the stomatal antechamber of P. radiata may contribute to mature-tree resistance to the needle pathogen, Dothistroma pini Hulbary.

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