Formation of tyloses in felled Quercus rubra L.

Summary Tyloses form in red oak (Quercus rubra L.) sapwood in a period of hours if the wood is cut during the active growth season and stored in green condition in the laboratory. If the wood is cut during dormancy and stored in green condition, tyloses form in a period of months. Electron microscopic examination reveals that the wall of a tylosis forms from a promonths. Electron microscopic examination reveals that the wall of a tylosis forms from a protective layer that develops inside the secondary wall of the ray cell in the vessel-ray pit-pair. Protective layers are also present in fiber-parenchyma pit-pairs. Protective layers may exhibit variable thicknesses, with light and dark layers alternating. A young tylosis wall consists of two layers: An electron-dense outer layer and an electron-transparent inner layer. Tyloses walls may attach to each other and form multilamellate tyloses. Sometimes the individual layers of tyloses walls appear lamellated. Because of the type of formation and structure, the tylosis wall in red oak apparently is a primary wall rather than a secondary. Tyloses walls have simple pits. The findings of this study enable felled hardwoods with potential for forming tyloses to be used without the destructive influence of tyloses.