Observations on Nectar Secretion in Fireweed,Epilobium AngustifoliumL. (Onagraceae)

Abstract

SummaryCapillary tubes were used to extract nectar accumulating in protected flowers of fireweed at various sites in coastal British Columbia. Mean sugar yields collected from individual flowers ranged from 0·66 mg/flower/day to 4·11 mg/flower day. Sixty four percent of the variation in daily yield was shared by different sites, suggesting that weather factors were of primary importance to nectar secretion patterns. Sunshine and mean temperature demonstrated the best correlations with nectar yield, explaining 62% and 63% of the variation, respectively. Flowers on plants defoliated 90% secreted an average of 68% of the sugar secreted by control flowers over a 3 day period, suggesting that stored phatosynthate was mobilized for secretion as nectar. Measurements of nectar secretion in a controlled environment under conditions of saturated photosynthesis revealed that variations in temperature alone could influence yield significantly. Mean yields of sugar collected under conditions of constant temperature ra...