Biology Reference
In-Depth Information
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Tropaeolaceae: sepal spur (Rachmilevits & Fahn, 1975)
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Verbenaceae: corolla tube (Smets, 1986)
Within the monocots, trichomes in tepal nectaries have been observed
occasionally, e.g., in Orchidaceae (Galetto et al., 1997; Stpiczyńska et al.,
2005) and Liliaceae (Kanikhi & Persson, 1997; Rudall et al., 2000). Smets
et al. (2000) mention trichomes in
Sisyrinchium
(Iridaceae), although uncer-
tain if they are nectariferous or not.
Other epidermal nectaries are small secreting glands or nectarioles (Vogel,
1998a), e.g., in the tepals of some Aristolochiaceae, Calycanthaceae, and
Cabombaceae, the sepals of one species of Gentianaceae, the perianth of
Nepenthaceae and Lentibulariaceae, the perianth and ovary wall of Sarrace-
niaceae, and the bracts and tepals of Cephalotaceae.
In some groups, trichomes and papillae are related to mesenchymatic
nectaries and are located in the epidermis of the nectary, e.g., in Aizoaceae
(Ihlenfeldt, 1960), Caryophyllaceae (Zandonella, 1977), and Polygonaceae
(Decraene & Smets, 1991a).
Nectar exudation.
There are several ways in which nectar can be exuded
though epidermal cells (Fahn, 1979, 1988; Pacini et al., 2003):
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Crossing the plasmatic membrane and the cell wall, accumulating between
the cell wall and the cuticle, which breaks under the nectar pressure
(Wunnachit et al., 1992).
•
The cell walls may have ingrowths like transfer cells that facilitate secre-
tion (Kronestedt et al., 1986).
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Through the cuticle, either with rupture of its outer layer (Figueiredo &
Pais, 1992; Stpiczyńska, 2003), or through microchannels or micropores
(Robards & Stalk, 1988; Vassilyev & Koteyeva, 2005; Wist & Davis,
2006).
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The epidermal cells gradually die, producing nectar for a given period
(Vesprini et al., 1999).
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Through orifices or small pores (Vogel, 1997).
•
Through modified stomata which have lost the capacity to open and close
(Fahn, 1988; Davis & Gunning, 1992; Gaffal et al., 1998); they are named
sap-holes (Vogel, 1997), nectarostomata (Smets, 1988), or nectarthodes
(Schmid, 1988).
Modified stomata are the most frequent way of nectar exudation and have
been extensively reported for many dicots: Apocynaceae (Galetto, 1997),
