FLORAL NECTARY STRUCTURE, AND NECTAR COMPOSITION IN ECCREMOCARPUS SCABER (BIGNONIACEAE), A HUMMINGBIRD-POLLINATED PLANT OF CENTRAL CHILE

Surface features, anatomy, and ultrastructure of the floral nectary of Eccremocarpus scaber (Bignoniaceae), pollinated predominantly by the largest-known hummingbird (Patagona gigas gigas), were studied togethe r with nectar sugar content and secretion rate. The annular disk necta ry comprises epidermis, secretory and ground parenchyma with intercell ular spaces, and branched vascular bundles terminating in the secretor y parenchyma where only phloem is found. Amyloplasts and vacuoles incr ease in size throughout development, the latter becoming sites of orga nelle degradation. Transferlike cells in nectary phloem and P-proteinl ike fibrillar material in phloem parenchyma were observed. Flowers pro duced around 32 mu l of nectar (mostly after anthesis) with ii mg of s ugar composed of fructose, glucose, sucrose, and maltose in a ratio of 0.34:0.32:0.17:0.17. Morphological studies as well as the presence of maltose and glucose in nectar suggest storage of the originally phloe m-derived sugars as starch with its subsequent hydrolysis. The low suc rose/hexose ratio (0.25) and high nectary secretion force (nectar per flower biomass) observed places E. scaber close to large-bodied bat-po llinated plants. A hypothesis based on nectar origin and nectar secret ion is advanced to explain pollinator-correlated variation in sucrose/ hexose ratio.