A theoretical flow model shortly to be published elsewhere describes the rate of axial flow of liquids, through conifer wood in response to known pressure differentials. This is based on certain assumptions as to the structure and ultrastructure of wood. The model predicts very different flow conditions for earlywood and latewood cells. While these predicted conditions are approximately similar to those observed experimentally by tree physiologists, it is not yet clear what advantages the reduced conductivity of latewood cells could convey to the tree.