Role of tyloses in the durability of chestnut oak

Tyloses are extruded cell contents of adjoining parenchyma cells that result in the obstruction of vessels. The function of tyloses in live trees is uncertain, but it has been proposed that they increase the natural durability of the wood by limiting water movement and the probing of fungal hyphae. Chestnut oak (Quercus montana, aka Quercus prinus) is inconsistent in producing tyloses; an initial study indicated a wide variation in the frequency of tyloses within and between trees of chestnut oak from three different states: VA, TN, and PA. This naturally occurring variation in tylosis abundance provides an opportunity to evaluate the impact of tyloses on natural durability. In this study, samples were further examined for extractive content, rate of wetting, and natural durability, to determine if these properties were related to the prevalence of tyloses. Tylosis abundance was not related to the density or extractive content but appeared to reduce water uptake, and fungal decay in laboratory tests. The mechanism of tyloses' role in reducing decay is unclear but may include reducing water and/or fungal hyphae movement through the vessels.