Anomalous Reaction Fibers in the Woody Monocotyledon Xanthorrhea australis R. Br

Abstract

This study of leaves, of the woody monocotyledon Xanthorrhoea australis, relates their progressive growth in length to associated differentiation of cells with apparently significant structural functions. It connects features of development of the readily identifiable cell wall layers, and the in-built axial shape of the growing leaves, as their positions of articulation move across the top of the shoot apex to the side of the stem.

Results show that the shape of the leaves, as developed with their growth in length, ensures their upper and lower faces will be exposed to light, when normal progressive movement of their positions of articulation takes them from the centre to the outside of the axial bundle of developing leaves. The study indicates also that the exposure occurs prior to differentiation of so-called 'reaction wood' cells, previously suggested as causing it. Furthermore, evidence of all changes in axial profile of the leaves through to senescence revealed no bending of leaves induced by the so-called reaction cells. The data suggest that those cells are differentiated to stiffen the leaves against excessive bending under gravity forces.