Biology Reference
In-Depth Information
•
Vogel (1977) suggested (a)
mesenchymatous
nectaries (consisting of
glandular and storage tissues that usually secrete nectar into interstitial
spaces or the cell wall apoplast and then exude it via modified stomata),
which certainly is the most widespread nectary type (Davis, 2003), (b)
epithelial
nectaries (consisting of a permeable, glandular epidermis often
with an underlying glandular tissue), and (c)
trichomatous
nectaries (con-
sisting of secreting glandular trichomes often aggregated into cushions).
Vogel supported this categorization according to histological structure and
the way of secreting the nectar to the plant surface.
•
Fahn (1979) identified nectaries exuding nectar (a) from
morphologically
unchanged epidermal cells or trichomes
(unicellular or multicellular),
(b) from
stomata
, (c) from
septal nectaries
, or (d) from
lysigenous cavi-
ties
, based on the anatomy and ultrastructure of the nectaries and their
mode of secretion.
•
Smets (1986, 1988) and Smets and Cresens (1988) proposed (a)
nectaria
caduca
(caducous nectaries related to falling floral parts: caducous sepals,
petals, and androecium), and (b)
nectaria persistentia
(persistent nectaries
related to non-falling floral parts: persistent sepals, receptacle, and gy-
noecium, including
gynopleural
or septal nectaries), which are associated
with non-homologous floral morphomes (Smets et al., 2000). The fate of
the organs where the secretory tissue is located was taken into account for
this classification.
Turning to more detailed topographic nectary classifications, several have
been published (e.g., Bonnier, 1878; Ewert, 1932; Brown, 1938; Fahn, 1953,
1979, 1982; Daumann, 1970), and undoubtedly many more can be formu-
lated.
In my opinion, Schmid's (1988) scheme is simpler than other classifica-
tions and, as it is based on strictly positional criteria, extremely practical,
covering most requirements to categorize nectaries. Schmid (1988) proposed
that only when experimental or observational evidence was available, could
a functional classification like Delpino's (1868-1875) be used; otherwise, it
seems preferable to adopt a topographical classification. On the other hand,
the strict application of rigid definitions is not always easy, and the broader
the categories are, the better. Occasionally, nectaries may, for example, be
located on the hypanthium and stretch towards the filament bases, or con-
tinue from the filament bases onto the receptacle and even the ovary base. In
such cases, it will be difficult to place them in any single category. Here, an
author should describe the nectaries fully instead of resorting to a category
that does not define the situation clearly.
