Fibre length, as a function of radial or tangential distance from a vessel was estimated from serial cross sections. This new method is easier and faster than earlier methods which rely on photographic prints of transverse images for the analysis. When necessary virtual tangential and radial sections were produced from 3D data to enable fibre length estimation. Fibre length up to the 5th and 2nd fibres away from a vessel in radial and tangential directions, respectively, were significantly shorter than fibres at greater distance from the vessels. Fibre length strongly correlated with radial vessel distance (r = 0.83) up to the 5th fibre and then leveled off. Vessel-adjacent fibres on the radial or tangential side of a vessel did not significantly differ in length. However, the rate of length increase differed significantly in the radial and tangential directions. Percentage of contact with rays varied independently of fibre length.
Paper quality depends on fiber diameter and wall thickness, and their derivatives. Fiber deformation occurs due to pressure from the vessel during development. The diameter and wall thickness of the fibers were measured following the direction of pressure exerted by the vessel on the face of the fiber cells. Fiber cell diameter measured perpendicular to and parallel with vessel enlargement was referred to as radial and tangential diameter, respectively, and likewise for fiber wall thickness. Differences in radial and tangential diameter and wall thickness of fiber cells in relation to their distance from vessels were analyzed. The radial diameter of fibers adjacent to large vessels decreased from the first to the fifth fiber, and from the first to the second fiber adjacent to small vessels. Conversely, tangential fiber diameter increased from the first to the fifth fiber for fibers adjacent to large vessels, and from the first to the second fiber adjacent to small vessels. The fibers adjacent to the vessel seem to have thicker walls in both the tangential than radial directions up to 2 and 5 fibers for small and large vessels, respectively. The first two fibers adjacent to small diameter vessels may produce higher strength paper than those up to five fibers from large diameter vessels, because the Runkel ratio, Coefficient of rigidity and Muhlsteph ratio values of fibers adjacent to small vessels are lower than fibers adjacent to large vessels. The opposite occurs for flexibility coefficient values.
Variation in fiber diameter and wall thickness was analyzed, with respect to the distance from xylem vessels in tangential and radial directions, using images containing the largest diameter along individual fibers from serial sections. For the diameter of the fibers around the vessel, it was often difficult to make a measurement in the radial and tangential direction, because of deformation. Then, around a vessel, we measured the fiber lumen diameter along the radial and tangential axes of the adjacent vessel. These are respectively referred as direction perpendicular to vessel enlargement (PnVE) and parallel with vessel enlargement (PrVE), as the enlarging vessel apparently accounts for the directionality of this fiber deformation. The change in cell wall thickness of individual fibers was also measured from the serial cross sections. Fibers adjacent to vessels were significantly wider in diameter and had thicker cell walls in the PrVE than those that were more distant from vessels in both radial and tangential directions. Wall thickness along the fiber length was found to vary in both fibers adjacent to and distant from the vessel, whereby wall thickness was greatest at the center, and gradually decreased towards the tip of the fiber.