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.

Vestured Pits: Do They Promote Safer Water Transport?

“…Tyloses are, for instance, a common feature in Fuchsia excorticata (Onagraceae), in which intervessel pits are always vestured, but the vessel-ray pitting is more rounded and frequently devoid of vestures (Butterfield and Meylan 1973). Moreover, Foster (1967) suggested that the vestures and pit membranes are broken down by enzymes secreted from the ray cell protoplast before tylosis extension takes place.…”

“…This may be a slight indication that formation of tyloses is prevented in taxa with vestured pits. Tyloses are usually not observed in association with ves- tured pits (Foster 1967;Meylan and Butterfield 1974), but there are certainly exceptions (e.g., Robinia, Fabaceae). In several taxa, pits between a vessel and a ray parenchyma cell can be vestured, partially vestured, or nonvestured on the vessel side, depending on the size and shape of the vessel-ray pits.…”

Control of Vascular Sap pH by the Vessel-Associated Cells in Woody Species (Physiological and Immunological Studies)

“…The term VAC was used for the first time in the 1960s to refer to the specialized cells surrounding the vessels in Robinia that are derived from both radial and axial xylem mother cells (Czaninski, 1964(Czaninski, , 1968. This cellular type has since been described in severa1 herbaceous and woody species (Foster, 1967;Czaninski, 1972Czaninski, , 1977Fujita et al, 1975;Catesson et al, 1982).…”

Submicroscopical Features of Leaves of Xyris Species

“…In X. hymenachne (Fig. 4), the walls of the stomata guard cells were covered internally by a special layer, called protective layer (O'Brien, 1970) or secondary cellulosic layer (Czaninskiy, 1973), which was reported for the parenchymatous cells of the secondary xylem by Barnett et al (1993), Chaffe (1974), Foster (1967 and Wisniewski & Davis (1989). Such a protective layer formed electron dense ramified clusters (Fig.…”