Fine structure of Tyloses in three species of the Myrtaceae

Abstract

The tylosis wall in Eucalyptus obliqua L'Herit. is shown to be composed of two microfibrillar layers. The outer layer (T1), with randomly orientated microfibrils, is covered with amorphous granular material. The inner layer (T2) is multilamellate. In sclerosed tyloses of E. miniata A. Cunn., each lamella of T2 is composed of many layers of microfibrils. Simple pits, delineated by circumferentially orientated microfibrils, are found in both sclerosed and non-sclerosed tyloses. The tylosis in E. obliqua is shown to arise from a two-layered structure formed within the secondary wall of the ray cell. This layer extends into the pit chamber, covering the pit membrane on the ray side. Following the breakdown of the vestures and the pit membrane, this double layer bulges out into the vessel to form the tylosis.