The two upper
petals of the common Pelargonium are thus marked near their bases; and I
have repeatedly observed that when the flowers vary so as to become
peloric or regular, they lose their nectaries and at the same time the
dark marks. When the nectary is only partially aborted, only one of the
upper petals loses its mark. Therefore the nectary and these marks
clearly stand in some sort of close relation to one another; and the
simplest view is that they were developed together for a special
purpose; the only conceivable one being that the marks serve as a guide
to the nectary. It is, however, evident from what has been already said,
that insects could discover the nectar without the aid of guiding marks.
They are of service to the plant, only by aiding insects to visit and
suck a greater number of flowers within a given time than would
otherwise be possible; and thus there will be a better chance of
fertilisation by pollen brought from a distinct plant, and this we know
is of paramount importance.
The odours emitted by flowers attract insects, as I have observed in the
case of plants covered by a muslin net. Nageli affixed artificial
flowers to branches, scenting some with essential oils and leaving
others unscented; and insects were attracted to the former in an
unmistakable manner. (10/3. 'Enstehung etc. der Naturhist. Art.' 1865
page 23.) Not a few flowers are both conspicuous and odoriferous.
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