NECTAR PRODUCTION AND PRESENTATION - Nectaries and Nectar - page 194

Table 5. Advantages and disadvantages of exposed and partially or completely protected nec-
tar. In the case of exposed nectar, evaporation may positively or negatively affect the response
of pollinators, thus facilitating different types of consumers.

Advantages Disadvantages

• Nectar may be collected by several
types of pollinators because it is acces-
sible.
• Nectar concentration varies with
temperature and RH and is therefore
suitable for different pollinators.
• Photosynthetic nectary parenchyma
receives enough light to be autono-
mous for carbohydrate synthesis.

• Nectar can be easily plundered.
• Nectar concentration is profundly af-
fected by environmental parameters;
nectar may crystallize due to evaporation
and cannot be collected.
• Fungal spores, bacteria, and airborne
material may fall into the nectar, trigger-
ing infections and damage in the absence
of antibiotic devices.
• Rain and heavy mist may remove nec-
tar or dilute it.
• Nectar reabsorption is difficult or
impossible because of evapora-
tion.

• Nectar concentration is relatively
unaffected by environmental parame-
ters.
• Nectar is protected from fallout of
airborne material.
• Nectar is not removed by rain or
mist.

• Nectar guides become necessary to
advertise its presence.
• Nectar may be accessible to only one
type of pollinator: species-specific polli-
nation.
• Photosynthetic nectary paren-
chyma receives little light if
shaded by floral parts.

• Nectar concentration is relatively
unaffected by environmental parame-
ters.
• Nectar reabsorption may occur over a
long period because evaporation is
limited.
• Nectar is not removed by rain
or mist.

• Nectar collected in the spur may be
stolen by animals with mouthparts that
can pierce the spur wall.
• Nectar is accessible only to a few pol-
linators having specialized mouthparts.
• Number of potential pollinators de-
creases with increasing spur length.

Nectar always comes to the surface of the nectary in microdrops, irre-
spective of its manner of secretion, whether secreted by modified stomata
that have lost their capacity to open and close (Davis, 1997), formed at the
tip of secreting hairs (as in many Malvaceae and some Cucurbitaceae, e.g.,
Cyclanthera , Sechium ), or derived from degeneration of single cells as in
Helleborus (Vesprini et al., 1999) (Fig. 3). These microdrops successively
fuse to form bigger drops that remain in situ (Fig. 4), slide down a vertical
surface, or form a flat surface.