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.