Morphology, Anatomy, and Relationship of Extrafloral Nectaries and Hydathodes in Two Species of Impatiens (Balsaminaceae)

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Abstract
Nectaries and hydathodes were studied in I. scabrida and I. balfourii (Balsaminaceae), 2 Himalayan natives. In I. balfourii a pair of equal, ovoid nectaries occurs in the stipular position at each node; in I. scabrida a shelflike nectary occurs in the stipular position on 1 side of the petiole base, with poorly developed nectary tissue on the other side. A core of small, isodiametric, closely packed cells and large raphide bearing idioblasts occupies the central portion of each nectary. In both species, the foliar nectaries on the proximal 3 or 4 pairs of leaf teeth are round to elongate and are similar internally to the larger nectaries. Both types are vascularized to some extent, primarily with phloem. Hydathodes occur on all leaf teeth distal to those bearing nectaries; they are vascularized with xylem elements that terminate about the midpoint of the tooth beneath an area of open stomata on the adaxial surface. Structures intermediate between nectaries and hydathodes are present in I. balfourii but not in I. scabrida. It is believed that Impatiens nectaries originated from hydathodes. Nectar was analyzed using gas chromatography. Floral nectar from both species contains nearly equal concentrations of fructose, glucose, and sucrose. The stipular nectar of I. scabrida is glucose dominant.