ALTERNATIVES TO THE ASSESSMENT OF EARLYWOOD AND LATEWOOD IN DICOTYLEDONOUS TREES: A STUDY OF STRUCTURAL VARIATION IN GROWTH RINGS OF APPLE ( MALUS PUMILA MILL.)

S ummary Several indices describing the variation in wood structure within growth rings of dicotyledon trees were examined in apple ( Malus pumila Mill.) scions grafted on to four rootstocks of different vigour. The cross‐sectional dimensions of 9600 fibres and 7200 vessel elements were measured in each rootstock and scion combination. Indices incorporating lumen width and wall thickness of fibres varied more or less linearly across growth rings, so that assessment of latewood could be made only by selecting some arbitrary limit, which may not be suitable for all rootstocks. The patterns of variation in vessel lumen area within growth rings varied markedly between rootstocks, and gave no clear indication of the point in the ring at which latewood formation might begin. A less extensive study of the distribution of tissues in the xylem at five positions across a growth ring showed that there tended to be a prominent reduction in the proportion of vessels, and an increase in the proportion of fibres between 10 and 30% of the distance across the ring. It was concluded that the concept of earlywood and latewood is not helpful to fundamental studies of wood structure and formation, and that in industry, measurement of relevant properties, such as the density of wood or fibres, may be made as easily as the determination of proportions of earlywood and latewood, however these wood zones be defined.