The floral nectary of Vicia faba L. (faba bean, broad bean, or field bean) consists of a disk which bears a long, basal, tapered projection. Large, open stomata, located at the tip of the projection, probably serve as exits for nectar. Phloem is present in the floral nectary. The extrafloral nectary consists of numerous secretory and nonsecretory trichomes aggregated on the abaxial surface of each stipule. Both xylem and phloem are present in the stipule beneath the extrafloral nectary. In both nectary types, large companion cells accompany the phloem. Epidermal and parenchyma cells of the floral gland, as well as the companion cells, develop wall ingrowths and are therefore transfer cells. Ultrastructural evidence suggests a granulocrine mechanism of nectar secretion in the floral nectary, wherein both apoplastic and symplastic routes for prenectar movement and escape appear feasible. Floral and extrafloral nectar differ in sugar concentration and in the predominance of sucrose, both of which are higher in exudate from floral nectaries.
The floral nectaries of Brassica napus L. (Argentine or Swede rape) consist of two pairs of glands which are supplied by phloem only. The lateral pair has an extensive phloem supply and produces most of the flowers' nectar, whereas the median pair is supplied by limited phloem and produces relatively little nectar. Because both lateral and median nectaries contain cells exhibiting similar structural features, the disparity in phloem supply between them could account for the observed difference in nectar production. Ultrastructural evidence suggests an energy-requiring, eccrine mechanism of nectar secretion in Brassica napus. Both apoplastic and symplastic routes for nectar movement and escape appear feasible. Stomata on the nectary surfaces may serve as exits.
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