Nectar production in Saponaria officinalis and in five species of Silene (S
. alba, S. dioica, S. noctiflora, S. nutans, S. vulgaris) was examined duri
ng two consecutive years (May to July 1993, and May to lune 1994) in the Bo
tanical Garden of the University of Giessen. Nectar volume and sugar concen
tration were studied in relation to time of day, flower sex, flower age, an
d flowering stage. Nectar amount in all species studied (except S. dioica)
increased in the afternoon or in the evening until midnight (or until the e
arly morning in S. nutans). After midnight and until midday, nectar volume
in non-visited flowers (except S. dioica) decreased. Nectar volume in non-v
isited S. dioica flowers increased constantly with flower age, indicating a
stable nectar secretion rate, possibly favouring both day- and night-activ
e flower visitors. Even at the time of highest nectar secretion, all specie
s studied presented several nectarless flowers. Sucrose dominance in the ne
ctar of the nocturnal species S. nutans and Saponaria officinalis fits well
with the general syndrome of flowers pollinated by hawkmoths. The syndrome
also applies to the nocturnal but regularly selfing, S. noctiflora. The mo
re generalistic species S. dioica and S. vulgaris, which are regularly visi
ted by bumblebees as well as nocturnal moths, secreted hexose-dominant nect
ar. Unexpectedly, Silene alba, the only nocturnal species that strictly exc
luded day-active flower visitors by closing flowers during the day, also se
creted hexose-dominant nectar. In some cases, nectar volumes and nectar con
centration differed significantly between hermaphroditic, male, and female
flowers. Female flowers of S. alba, S. dioica, and S. nutans contained sign
ificantly less concentrated nectar than male or hermaphroditic (S. nutans)
ones. In S. noctiflora and S. vulgaris the difference was not statistically
significant but nectar concentration did show the same tendency.