Question

Trunks of some of the aged tree species appear to be composed of several fused trunks. Is it a physiological or anatomical abnormality? Explain in detail.

Answer 1

Formation of annual ring

During the early stages a non-continuous (in patches) layer of meristematic plant tissue is found between xylem and phloem. After gaining maturity these patches separate and develop vascular tissues, which are named as vascular cambium. They give rise to cambial rings in plants.

In dicot stems, primary xylem and phloem are separated from each other by the presence of cambium cells called intrafascicular cambium. At the time of secondary growth, cells of medullary rays (strips of parenchyma separating xylem and phloem bundles) become meristematic to form interfascicular cambium. Now both the cambium i.e, interfascicular and intrafascicular form a continuous ring-like structure known as a cambial ring.

The cells of the cambial ring undergo mitotic division and produce secondary phloem and secondary xylem. The older phloem gets discarded and new secondary phloem becomes functional, secondary xylem and wood persists.

Two types of woods spring (earlywood) and winter (latewood) are formed and they together form the annual rings of the tree.

When the section of the aged tree is cut, these annual rings appear to be formed by the fusion of several trunks. Thus, the fused trunks are due to anatomical abnormality of secondary growth.