Contact and non-contact proportions between axial elements and rays

Proportions of axial elements without any spatial contacts with rays were investigated. Non-contact rates between rays and fusiform initials or axial parenchyma strands were examined in tangential sections of cambial or axial parenchyma zones in 21 hardwood species. The non-contact rates were very different among species, ranging from 0% to 76%. Serial transverse sections of xylem were used to determine the non-contact rates between rays and wood fibers in 3 of the 21 hardwood species having high non-contact rates of parenchyma strands. The non-contact rate of wood fibers was 49% in Albizia julibrissin (non-storied cambium), 30% in Paulownia tomentosa (non-storied cambium), and 52% in Pterocymbium beccarii (storied cambium). Tangential sections of three softwood species, Pinus thunbergii, Cryptomeria japonica, and Chamaecyparis obtusa were used to investigate the contacts between rays and tracheids. All tracheids in the three species had contact with at least one ray, ranging from 1 to 15 rays.