Developmental anatomy of natural root grafts in Ficus globosa

The series of events, and the anatomical changes connected with them, leading to the fusion of aerial roots in Ficus globosa Blume are described. The initial contact between two aerial roots is estabiished by the formation and fusion of epidermai hairs. Secondary growth increases the size of the roots, and consequently the cortices of the two adjacent roots approach one another and become compressed. The cortical tissues thin out in the central region of the compressed zone, but fuse marginally and remain intact. In both roots the ray cells near the contact area become highly meristematic; by active division they produce many parenchyma cells that extend towards each other and finally merge to establish a continuous parenchymatous zone between the steles of the two roots. The cortical tissues, secondary phloem, and vascular cambium in both roots are interrupted by the formation of this new tissue. Later some of the parenchyma cells below the fused regions of the cortex redifferentiate into vascular cambium and extend laterally, joining the pre-existing, interrupted cambia of the two roots. Thus a continuous ring of vascular cambium is reorganized that gives rise to more secondary xylem and phloem. Cork cambium differentiates in the subepidermal layers to form a thick periderm with a smooth surface, so that the fused roots appear externally as a single root. Certain important points of the present study are discussed with reference to previous work.