The Coralloid Roots of Macrozamia Communis L. Johnson

Abstract

Macrozamia communis exhibits root dimorphism, possessing both normal and coralloid roots. The latter are pneumatophores in which an algal zone may be present or absent. In the coralloid roots the root cap tissue was interpreted as forming a secondary cortex which persisted throughout the life of the root. Underlying the secondary cortex was a transformed epidermis, the cells of which, following the establishment of algae within the intercellular spaces, elongated radially to form an algal zone easily visible to the eye. Nostoc-like blue-green algae were isolated from this zone. In the absence of algal infection the transformed epidermis remained inconspicuous. The root cap anatomy of the normal roots was similar to that described for other gymnosperms. The tips of the alga-free coralloid roots were characteristically located near the soil surface. The alga-containing coralloid roots were less strictly negatively geotropic and were found at depths up to 30 cm below the soil surface.