Interfiber bordered pits

Figure 23. SEM of spiral thickenings in the fibers of Douglas-fir wood radial surfaces. Key A, spirals in the vicinity of ray cross-field pits in early wood and B, nigh magnification of spirals in the last latewood fiber of one year and the first earlywood fiber of the next year. Pits shown in B are interfiber-bordered pits.

Within a growth ring, softwood interfiber pits are larger and more abundant in earlywood. In latewood they are fewer, smaller, and often appear slitlike in very thick-walled fibers (2). This same type of pit in hardwood fibers varies morphologically with the fiber type, changing from an obviously bordered pit in thin-walled cells to only a slitlike aperture in fibers with thick walls. 

Copyright 1982, American Chemical Society.) (A) SEM of interfiber pits in earluwood as seen on the wood radial face. Note the donut-shaped borders. (B and C) SEM of pit pairs between adjacent fibers cross-sectional suiface. (D) SEM ofbordered-pit membranes (PM) in face view of a split wood radial surface. (E) Light micrograph of pit pairs as seen in cross section with a light microscope. Key PM, pit membranes PB, pit border and PA, pit aperture. 

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