New concepts and terminology of coniferous periderms: necrophylactic and exophylactic periderms

Abstract

Field observations were made on wound and pathological periderms, regardless of the causal agent, and periderms formed at abscission zones, old resin blisters and rhytidomes in Abies amabilis (Dougl.) Forbes, Abies grandis (Dougl.) Lindl., Tsuga heterophylla (Raf.) Sarg., and Thuja plicata Donn. It was established that these periderms were of reddish-purple sequent periderm (rsp) type, rather than either the brown first periderm (bfp), or brown sequent periderm (bsp) types. These reddish-purple pigmented periderms, like the rsp (the usual sequent periderm) were found abutting necrotic tissues and were moreover identical with rsp in 15 newly demonstrated cryofixation and chemical characteristics. Because of this equivalence, it is proposed that all these reddish-purple periderms, including the usual sequent periderm (rsp), constitute one category, the necrophylactic periderms. These periderms arise whenever regeneration of a periderm after death of cells is required, and their main function seems to be protection of living tissues from the adverse effects associated with cell death. Because of the equivalence of bfp and bsp, they constitute another category, the exophylactic periderms. This second category of periderms has a common function of protecting living tissues against the external environment.