Warty layer

Structure of the Cell Wall. The iaterior stmcture of the ceU wall is shown in Figure 6. The interfiber region is the middle lamella (ML). This region, rich in lignin, is amorphous and shows no fibnUar stmcture when examined under the electron microscope. The cell wall is composed of stmcturaHy different layers or lamellae, reflecting the manner in which the cell forms. The newly formed cell contains protoplasm, from which cellulose and the other cell wall polymers are laid down to thicken the cell wall internally. Thus, there is a primary wall (P) and a secondary wall (S). The secondary wall is subdivided into three portions, the S, S2, and layers, which form sequentially toward the lumen. Viewed from the lumen, the cell wall frequendy has a bumpy appearance. This is called the warty layer and is composed of protoplasmic debris. The warty layer and exposed layer are sometimes referred to as the tertiary wad. 

The cell wall is built up by several layers, namely (Figs. 1-12 and 1-13), middle lamella (M), primary wall (P), outer layer of the secondary wall (SJ, middle layer of the secondary wall (S2), inner layer of the secondary wall (S3), and warty layer (W). These layers differ from one another with respect to their structure as well as their chemical composition. The microfibrils wind around the cell axis in different directions either to the right (Z helix) or to the left (S helix). Deviations in the angular directions cause physical differences and the layers can be observed in a microscope under polarized light. 

Fig. 1-12. Simplified structure of a woody cell, showing the middle lamella (ML), the primary wall (P), the outer (Si), middle (S2), and inner (S3) layers of the secondary wall, and the warty layer (W) (Cote, 1967, with permission).

The warty layer (W) is a thin amorphous membrane located in the inner surface of the cell wall in all conifers and in some hardwoods, containing warty deposits of a still unknown composition. Each species has its own, characteristic warty layer. 

Warts. Warts are conelike or droplike protuberances, sometimes found covered with an amorphous deposition, that are scattered in a random pattern on the inner fiber-wall surface in most softwoods and the fibers of some hardwood species (Figure 24). The wart structure, known collectively as the warty layer (IT), is manufactured by the living cell protoplast before cell autolysis 18, 19). The warty layer is ligninlike in nature but has no apparent physiological role it prob-... 

Figure 24. TEM of warty layer in softwood (A) and hardwood (B) fibers direct carbon replicas. (A) Lumen surface of fiber in balsam fir. Note the amorphous substance masking the S3. (Reproduced with permission from Ref. 20. Copyright 1974, Society of Wood Science and Technology.) (B) Lumen surface of a warty fiber in sycamore. The slits shown here are pit apertures. (Reproduced with permission from Ref 23. Copyright 1974,...

Warts, The presence of a vessel element warty layer is species-dependent, and where it is found, it tends to be associated more with the occurrence of scalariform-type perforation plates (J, 23). As in the case of fibers, vessel warts have no obvious role at the cellular... 

Finally a thin warty layer may be deposited on the cell wall, which appears to be composed of proteinaceous or lignin-like material. Where present the warty layer completely lines the cell lumen and pit cavities. It is widely found in softwood tracheid elements. 

Figure 9.19. Schematic representation of cell-wall layers in a tracheid or fiber, with respective orientation of microfibrils illustrated by lines. ML, middle lamella, lignin P, primary wall Sj, S2, and S3, layers of the secondary wall W, warty layer. (Tsoumis, 1968, p. 69.)...

Figure 6.43 The cell walls of a tracheid or wood fiber have several layers, each with a different orientation of microfibrils (164). ML, middle lamella, composed of lignin P, primary wall S, Sj, S3, layers of the secondary wall VJ, warty layer. The lumen in the interior of the warty layer...

Liese W 1965 The warty layer. In Cote W A (ed) Cellular ultrastructure of woody plants. Syracuse University Press Syracuse, 251-269... 

The organization of a typical softwood tracheid or hardwood fiber is presented in Fig. 1. In the primary wall (P) the cellulose microfibrils form a disordered network, whereas the outer layer of the secondary wall (Si) has a crossed, fibrillar structure. The middle layer of the secondary wall (S2) represents the bulk of the cell. Here, the cellulose microfibrils run almost parallel to the fiber axis. The microfibrils in the inner layer of the secondary wall (S3), sometimes referred to as the tertiary wall, are oriented at a steep angle to the fiber axis. Toward the central lumen, the S3 layer is often terminated by a warty membrane. 

The exposed cell cavity may be warty in appearance microscopically. This layer consists primarily of metabolic byproducts and residue from the protoplast. 

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