THE FLORAL NECTARY OF DIGITALIS-PURPUREA L., STRUCTURE AND NECTAR SECRETION

The floral nectary of the foxglove (Digitalis purpurea L.), located at the base of the ovary, was examined by: scanning electron microscopy; quantitative bright-field microscopy via computer-aided 3-D reconstru ction from serial sections; morphometric procedures; transmission elec tron microscopy and measurement of nectar efflux under different exper imental conditions. Time-lapse video recording via a microscope with i ncident light clearly showed that the nectar escaped from the aperture s of modified stomata. The volume flux via individual stomatal apertur es was 0.31 +/- 0.1 nl min(-1); therefore only a fraction of the total number of stomata per nectary (115 +/- 8) would be sufficient to disc harge the amount of nectar reported in previous publications. The stom atal apertures are continuous with intercellular spaces traversing the small-celled nectariferous tissue. The latter is vascularized only by phloem, whose termini consists of rows of slender cells. These sieve- like cells are surrounded by more or less isodiametrical sheath cells with dimensions similar to the secretory cells. Details of nectary fun ctioning are based on enhanced structural information, complementary d ata on nectar discharge after experimental manipulations and the natur e of the effluence. (C) 1998 Annals of Botany Company.