The nature of reaction wood. IV. Variations in cell wall organization of tension wood fibres

Abstract

The cell wall organization, the cell wall texture, and the degree of lignification of tension wood fibres have been investigated in a wide variety of temperate and tropical species. Following earlier work describing the cell wall structure of tension wood fibres, two additional types of cell wall organization have been observed. In one of these, the inner thick "gelatinous" layer which is typical of tension wood fibres exists in addition to the normal three-layered structure of the secondary wall; in the other only the outer layer of the secondary wall and the thick gelatinous layer are present. In all the tension wood examined the micellar orientation in the inner gelatinous layer has been shown to be nearly axial and the cellulose of this layer found to be in a highly crystalline state. A general argument is presented as to the meaning of differences in the degree, of crystallinity of cellulose. The high degree of crystallinity of cellulose in tension wood as compared with normal wood is attributed to a greater degree of lateral order in the crystalline regions of tension wood, whereas the paracrystalline phase is similar in both cases. The degree of lignification in tension wood fibres has been shown to be extremely variable. However, where the degree of tension wood development is marked as revealed by the thickness of the gelatinous layer the lack of lignification is also most marked. Severity of tension wood formation and lack of lignification have also been correlated with the incidence of irreversible collapse in tension wood. Such collapse can occur even when no whole fibres are present, e.g. in thin cross sections. Microscopic examination of collapsed samples of tension wood has led to the conclusion that the appearance of collapse in specimens containing tendon wood can often be attributed in part to excessive shrinkage associated with the development of fissures between cells, although true collapse does also occur. Possible explanations of the irreversible shrinkage and collapse of tension wood fibres are advanced.

Tree growth stress and related problems

“…10) [57]. In the case of rather primitive angiosperms like Magnoliaceae, large cellulose content and low MFA seem to produce a similar effect as the formation of distinctive G-layer in highly evolved eudicot species [43]. However, the magnitude of tensile L stress in tension wood of those primitive species is somewhat lower than in typical tension wood of highly evolved eudicots species.…”

“…The G-layer is very poorly lignified and contains highly crystallized microfibrils, orientated almost parallel to fiber axis [43]. In tension wood, the L stress possesses a very large value.…”

Drought tolerant stem anatomy characteristics in Manihot esculenta (Euphorbiaceae) and a wild relative

“…Gelatinous fibers are usually related to the formation of reaction wood, which is the development of fibers in their differentiating xylem by an additional layer at the inner face of the secondary wall in response to gravitational stimuli whose function is to sustain mechanical strength (Dadswell and Wardrop, 1955;Wardrop and Dadswell, 1955;Evert, 2006). As the materials studied do not form reaction wood, it is believed that these fibers are involved in water retention, making them more resistant to drought.…”

An Overview of Microfibril Angle in Fiber of Tension Wood

“…2B, 3B) [33][34][35][36][37][38]. In some species having no G-layer in reaction wood, it has been reported that microfibril angle of S2 layer decreased [15,[39][40][41][42] reported that the microfibril angle of S2 layer was very small (5 to 10 degrees) in reaction wood of Magnolia acuminate and Liriodendron tulipifera.…”