Morphological and Anatomical Observations of Adventitious and Lateral Roots of Sago Palms

摘要

Sago palm (Metroxylon sagu Rottb.), which produces starch in large quantities in its trunk, could become one of the most important nutritious food resources in the near future. Although its root functions are thought to be very important for the enormous shoot growth, the morphological and anatomical studies are limited. This study investigates external and internal structures of sago roots with reference to their functions to distinguish two types of roots in each plant; i.e., large (about 6-11 mm diameter) and small (about 4-6 mm diameter) roots. Large roots were adventitious roots whose primordia were formed just inside the epidermis in the stem, emerged from the trunk surface and grew downward into the soil. Small roots were lateral roots whose primordia were formed on large roots running horizontally or on other small roots, grew not only downward and obliquely in both deep peat and mineral soils, but also right above in deep peat soils. Anatomical observations revealed that both large and small roots had the same internal structures containing epidermis, exodermis, suberized sclerenchyma .cells, cortex and stele, with only differences in their sizes or cell numbers. Both roots had characteristic development of schizogenous or lysigenous aerenchyma, but seem to have different functions. Root primordia were formed successively throughout the trunk. Root primordia in the lower trunk had a large diameter, while density of root primordia per unit trunk surface area was high in the upper trunk.