Flora Unveiled

424 i Flora Unveiled

Based on the writings of Camerarius, Linnaeus, and Koelreuter, Sprengel took it as a
given that pistils and stamens were sexual structures. As we saw earlier, Koelreuter’s discov-
ery of insect pollination led him to conclude that the primary function of floral nectaries
is to attract insect pollinators. Although insect pollination appeared at first glance to be a
random process, it is made purposeful by the insects’ continual search for nectar. In his 1761
paper Vorläufige Nachricht (Preliminary Report), Koelreuter had presciently predicted that
“(t)he decline of the insect [species] would inevitably be followed by the decline of the plant
species.”^40
Sprengel only learned about Koelreuter’s work on nectaries and insect pollination some
time after beginning his own studies.^41 Like Koelreuter, he came to regard insect- mediated
pollination as a divinely ordained arrangement to ensure the perpetuation of plant species.
His own brilliant entry into the field of pollination biology literally began with a splash—
the splash of raindrops on petals. He had been examining the petals of a type of geranium
(cranesbill) when he suddenly became curious about the many fine hairs inside the mar-
gins of the petals near the base, just above the nectaries, and “wondered what purpose they
might serve.” The introduction of his book begins with this insight:

When I carefully examined the flower of the wood cranesbill (Geranium sylvaticum)

in the summer of 1787, I  discovered that the lower part of its corolla was furnished

with fine, soft hairs on the inside of the margins. Convinced that the wise creator of

nature had not created even a single tiny hair without definite purpose, I wondered

what purpose the hairs might serve. And it soon came to my mind that if one assumes

that the five nectar droplets which are secured by the same number of glands are

intended as food for certain insects, one would at the same time not think it unlikely

that provision had been made for this nectar not to be spoiled by rain and that these

hairs had been fitted to achieve this purpose.^42

Sprengel found similar small hairs located at nearly the same location in other species of
Geranium. He therefore concluded that:

Since the flower is upright and tolerably large, drops of rain must fall into it when it

rains. But no drop of rain can reach one of the drops of nectar and mix with it, because

it is stopped by the hairs, which are just above the nectaries, just as a bead of sweat

which has run down a man’s forehead is caught by his eyebrows and eyelashes and is

prevented from running into his eye. An insect is not hindered by these hairs from

getting at the drops of nectar. ^43

In the flowers of every species he examined, Sprengel found comparable floral structures
that protected nectar droplets from rain, from which he inferred a functional relationship:

The longer I  continued this investigation, the more I  saw that flowers that produce

nectar drops are so contrived that insects can easily reach it, but that the rain cannot

spoil it; but I gathered from this that it is for the sake of the insects that these flowers

secrete their nectar, and that it is secured against rain so that they may be able to enjoy

it pure and unspoiled. ^44