The nature of reaction wood. VII. Lignification in reaction wood

Abstract

Lignification of reaction wood, caused to form in the stems of seedlings of Trisrania conferta K.Br., Grevillea robusta A.Cunn., Eucalyptus botryoides Sm., E. Melliodora A.Cunn. ex Schau., Hakea laurina R.Br., and Liquidambar styraciflua L., has been investigated with the use of ultraviolet microscopy and staining techniques. The polarizing microscope was used in a supplementary study of cell wall structure.

The "gelatinous" layer of reaction wood fibres undergoes lignification, the extent depending on whether the fibres are located in the middle or on the edges of areas of reaction wood. There is evidence for the diffusion outwards into the "gelatinous" layer of breakdown products of cell protoplasts. As the growing season advances, there is a progressive reduction in the number of cambium cells dividing to form reaction wood fibres. This process reaches its maximum expression in the deciduous species Liquidambar styraciflua, where there is a complete change-over to the production of normal cells at the end of the growing season.

The anatomical features of three areas of reaction wood caused to form in stems of Tristania conferta and Eucalyptus melliodora by orientating horizontally growing plants twice through 180° are described. They further emphasize the importance of the location of individual reaction wood cells in the stem in determining the structure of their walls and the pattern of wall lignification.

The results of staining sections for the enzyme peroxidase with benzidinehydrogen peroxide are described. They point to the need for closer investigation by direct methods of enzyme isolation and estimation.