Abstract
Two 10 years old Platanus occidentalis L. trees growing as copies had been fallen to study the variation in vessel element dimensions and specific gravity between and within the trees . Eight discs were cut from each tree from the stump until 14.30 m. with 2 m. interval between each disc. Also ,five wood specimens were taken from each disc from pith to bark at north direction .The results showed that the average vessel element length was 0.566 mm. , mean diameter was 79.45 micron, while mean specific gravity was 0.594. Average vessel elements length and diameter varied throughout stem lengths, there were an increase in these values from base to 2.30 m. height by which the highest mean values were presented (0.504 mm and 58.84 micron respectively ), then these values decreased up to the 8.30 m. height level followed by gradual increase to the 10.30 m. height level then it decrease to the last height level (14.30 m.). Specific gravity mean values decreased by increasing stem height levels , the highest mean was 0.649 at the stump level (0.30 m. ) and lowest value was 0.5541 at 14.30 m. height level. Variation of vessels mean length and diameter among stem diameter level was found to have an increasing values from pith to bark , the lowest mean value was at the pith ( 0.539 ml. And 74.539 micron respectively ), and the highest mean value was near the bark ( 0.612 mm and 85.o66 micron respectively ). There were decreasing in specific gravity mean values from pith toward the bark , the highest mean value was near the pith 0.619 and the lowest value was 0.561 near the bark. Also it was found that there were significant differences between the trees in vessel diameter and specific gravity, but there was no significant differences in vessel length between the trees.
