Biophysical basis for wall layer nomenclature

Abstract

Overall, the foregoing discussion of the interactions and effects of the several factors, which together determine the characteristics of the cell wall, suggest that it could be advantageous to reconsider the current basis of designating the wall layers in wood fibres as primary ‘P’ and secondary ‘S’, with successive subdivisions of S into S₁, S₂ and S₃, and even into transition zones, such as S_1,2 and S_2,3 between them. This is not to challenge the concept leading to identification of P and S, or the fact that polarized light and electron microscopy can show differences between S₁, S₂ and S₃. Rather it is to consider the significant consequences of unavoidable imprecision in respect of determining: (i) true boundaries between those subdivisions of the cell wall; (ii) the character of each layer; and (iii) the importance of the variations involved. The review is directed also to the practicability of removing some ambiguities in general concepts of cell wall formation.