STRUCTURAL ASPECTS OF CLUSTER ROOT DEVELOPMENT AND THEIR POSSIBLE SIGNIFICANCE FOR NUTRIENT ACQUISITION IN GREVILLEA-ROBUSTA (PROTEACEAE)

Light microscopy (LM), scanning (SEM) and transmission electron micros copy (TEM) were used to study structure and function of cluster roots in Grevillea robusta. These roots were developed during growth of G. r obusta seedlings in modified Hoagland's solution lacking phosphate. Cl uster rootlets formed root hairs, basipetally, only after completing t heir determinate development. The rootlet hairs branched in two ways a nd some had apical swelling. Rootlets with hairs produced two differen t forms of exudate, one fibrous and the other globular in nature. The fibrous material appeared to be synthesised in the cortical cells. It is released by exocytosis from the epidermis. Rootlet hairs produced o nly fibrous exudate. They attached firmly to pieces of vermiculite. Th e significance of cluster roots is discussed within the context of pat chy soil resources. (C) 1996 Annals of Botany Company