IN-VITRO ABSCISSION OF KAURI (AGATHIS-AUSTRALIS) BRANCHES

When nodal explants from tips of horizontal branches of seedling Agath is australis (Araucariaceae) are cultured in vitro, the distal 3 mm of internode progresses through a series of morphological and anatomical changes, and ultimately detaches. Changes include: desiccation; regio nal chlorosis; internode swelling associated with proliferation and ra dial expansion of cortical parenchyma; interruption of vascular contig uity by invading vascular parenchyma; necrosis and separation. Explant s from material older than one growth flush, and those from orthotropi c axes, do not exhibit this syndrome. Second-generation explants show internode abscission, regardless of age of parent material. The techni que may be a useful experimental system for studying branch cladoptosi s in woody species.