the variation of fiber length, vessel element length, relative density, ring width and the distribution o f juvenile wood within the stem of a 62-year-old trembling aspen (populus tremuloides michx.) were studied. samples from the stem where acquired at 0.15 m, 1.3 m and then at every 2 m interval thereafter and examined in the east and west aspects. radially, fibers and vessel elements both initially increased in length from the pith outwards and then remained relatively constant toward the bark. the vertical variation in cell length for both fibers and vessel elements was parabolic in shape. the anova found that the three-way interaction aspect x zone x height was significant for both mean fiber and mean vessel element length. for both cell types, the juvenile wood zone had significantly shorter mean cell lengths than the mature wood zone in both aspects, when comparing means from the same height. relative density did not have a radial variation common to all the heights. the vertical variation o f relative density was eccentric. the anova found that the two two-way interactions, zone x height and aspect x height, were significant. at heights where there was a significant difference, the mature wood zone had the significantly larger relative density. ring width was found to generally increase from the pith outwards. the juvenile-mature wood boundary was demarcated using the radial variation of fiber length. the radial variation of vessel element length was tested as a criterion as well and found to be a viable criterion for demarcating the juvenile-mature wood boundary. vertically, the width of the juvenile wood zone decreased with increasing height. the study tree consisted entirely of juvenile wood up to the age of 26. at age 62, the juvenile wood volume was 162 dm3 which represented 28.0 percent of the total stem volume. the volume of mature wood exceeded the volume of juvenile wood at age 53. the relationship between the percentage of stem volume and percentage of basal area that is juvenile wood varied from linear to curvilinear depending on the height examined. from heights 0.15 m to 5.3 m, the relationship was curvilinear, while above 5.3 m the relationship was approximately linear. the width of the juvenile wood zone, expressed as number of rings, had a strong negative linear correlation with the interval age at the pith. the width of the juvenile wood zone decreased as the interval age at the pith increased, suggesting an ageing effect on the cambial initials influences the duration o f juvenile wood production.