RESUMO
Root nodules were collected from the existing plantation of Casuarina equisetifolia from three different agroclimatic zones of Tamil Nadu, India. Morphological variation, histology, histochemistry and nutrient contents of the nodules were studied. The nodules were found to be simple, dichotomously branched and coralloid. The stele in simple and branched nodules reached up to the tip of the nodules. Structure of Frankia nodules was described using histochemical methods to elucidate the nature of micro-symbiont within the nodules. The nodule consisted of a distinct periderm enclosing the cortex. The cortex showed patches of infected cells interspersed among the uninfected ones. Inside the cortex was a stele bound by an endodermis, which contained high amount of tannin. The micro-symbiont was observed in the nodule tisues in hyphal form and spore packed sporocorp was also seen in the cortex. The histochemical tests revealed the presence of proteins, insoluble polysaccharides and polyphenols.