Growth strains and related wood structures in the leaning trunks and branches of Trochodendron aralioides - a vessel-less dicotyledon.

摘要

This study examined the anatomy and the peripheral distribution of released growth strains of leaning trunks and branches of Trochodendron aralioides grown in Taiwan. The relationships between anatomical structures of tension wood and growth strains of the leaning trunks and branches of this species are discussed. Leaning trunks and branches of T. aralioides, a primitive vessel-less dicotyledon, showed increased radial growth and gelatinous fibres on the upper side similar to the features found in dicotyledons with vessels. The patterns of peripheral longitudinal growth strain were variable among trees but similar at different heights within the same leaning trunk. Growth strains on the lower side of the trunks were very small but they are relatively large on the lower side of the branches. Growth stress in the branches was partly affected by the gravitational bending stress, which would be exerted mostly on the lower side. Large spring back strains of branches were associated with large surface strains. Both the microfibril angle (MFA) and the percentage area of gelatinous fibre showed positive relationships with the measured strains. The MFA of the S2 wall layer in tracheids in the opposite wood was 24.6+or-2.2 degrees , whereas the MFA of gelatinous layer in the tension wood was only 14.2+or-2.7 degrees . The difference of MFA between the gelatinous fibres and the opposite wood was one of the factors accounting for the large contracting force for reorientation..