The nature of reaction wood. VIII. The structure and differentiation of compression wood

Abstract

The cell wall organization of tracheids of natural and chemically induced compression wood of Pinus radiata and Actinostrobus pyramidalis has been shown to be the same, and is similar to that established in previous studies of natural compression wood. In the secondary wall only two layers were present. In the second of these there was a well-developed system of helical cavities, separating ribs of cellulose. The ribs of cellulose were parallel to the direction of microfibril orientation; were complex in form; and the cellulose lamellae lay parallel with the wall surface. A well-developed wart structure was present. During the differentiation of compression wood tracheids, the intercellular spaces were formed during the phase of surface enlargement of the differentiating tracheids. At an early stage the intercellular spaces appeared to contain cytoplasmic ground substance.

During the development of the layer S1 the cytoplasmic organization was similar to that of normal tracheids, the cells containing a large vacuole with a well-developed tonoplast and plasmalemma. During the development of the layer S2 the cytoplasm contained numerous small vesicles with no large vacuoles, and in many instances the plasmalemma was absent. At the conclusion of the differentiation of the cell the plasmalemma was again present and penetrated the helical cavities of the wall.

Compression wood induced by 3-indoleacetic acid (IAA) alone, gibberellic acid (GA) alone, or IAA and GA in combination was identical with that formed under natural conditions. The localized lateral application of IAA to vertical stems caused conspicuous bending of the stem as well as compression wood formation.