As one of the refractory softwood species, the major problems in the preservative treatment of spruce based on the radial flow relate to the anatomical structure of the wood material. The most important morphological features influencing this were the amount of the nature and the condition of both ray tracheids and ray parenchyma cells, and the cross-field pits in particular. The conducting pathways of Sitka spruce have been discussed elsewhere and it was suggested that both ray parenchyma cells and ray tracheids (in either uniseriate or fusiform ray tissues) offer the major flow path in the radial direction. In consequence therefore, the radial flow of preservative fluid: (1) is probably through the ray parenchyma cells to the longitudinal tracheids across cross-field pit apertures and then back again to the other ray parenchyma cells, (2) is associated by bordered pits leading from longitudinal tracheids to ray tracheids and then either semi-bordered or simple pits permitting flow to adjacent ray parenchyma cells, (3) is conducted by simple pit pairs from ray parenchyma cell to ray parenchyma cell.

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