414 i Flora Unveiled
Gmelin had been corresponding with Linnaeus about plant hybrids, and was preparing a
republication of Camerarius’s Epistola. In his 1749 inaugural lecture, Gmelin discussed the
possible origin of new species of plants and animals, either by hybridization or spontaneous
processes, and he underscored the need for further research in this area. Under Gmelin’s
influence, Koelreuter began to take an interest in the sexual theory of plants, especially the
question of plant hybrids, and, in 1752, while still a medical student, he published a sum-
mary of all the research conducted on the subject of plant sex since Camerarius. Gmelin
must have been impressed. In 1755, the year Koelreuter graduated, Gmelin used his connec-
tions to procure a position for his star pupil as custodian of the natural history collections
at the Imperial Academy of Sciences in St. Petersburg.^23
As discussed in Chapter 13, Linnaeus had won the prize offered by the Imperial
Academy for the best essay in support of the sexual theory. Koelreuter, who was then in
St. Petersburg, had always regarded Linnaeus as something of a dilettante compared to
Camerarius. Hoping to best the celebrated Swede at his own game, the young Koelreuter
had quietly begun his own experiments on plant hybridization, but he was unable to com-
plete his analysis in time to submit an essay for the contest. He was thus forced to watch
from the sidelines as Linnaeus garnered all the glory. Along with his essay, Linnaeus had
sent the Academy seeds of his Tragopogon hybrid, and Koelreuter was assigned the task
of confirming their identity. Based on his own preliminary results with tobacco hybrids,
he had already formed the opinion that true hybrids are always sterile and intermedi-
ate in form between their parents. Applying this criterion, he concluded that Linnaeus’s
Tragopogon hybrid was actually “only half a hybrid” because it was neither sterile nor
intermediate in appearance. (We will return to the meaning of “half a hybrid” later in
the chapter.)
Frustrated by his failure to submit an essay, Koelreuter redoubled his efforts, determined
to amass an overwhelming body of evidence that would dispel any lingering doubts about
the sexual theory. He pursued his hybridization experiments at St. Petersburg in 1760 and
1761, after which he returned to Germany. While journeying from town to town, he man-
aged to conduct experiments during brief stopovers: in Leipzig and Berlin in 1761, in Sulz
in 1762, and in Calw in 1763.^24 It was during this period of gypsy- like freedom that he pub-
lished three of his six landmark papers on plant hybridization.
In 1763, Koelreuter had the good fortune to come to the attention of the Princess
Caroline Louise, wife of Charles Frederick, Margrave of Baden. Princess Caroline was a
brilliant, multitalented woman, fluent in five languages, and well- versed in the arts and sci-
ences. She corresponded with both Voltaire and Linnaeus and made her palace at Karlsruhe
into one of Germany’s premier cultural centers.^25
An early admirer of Linnaeus, Princess Caroline’s knowledge of botany was judged to
be the equal of any professor’s. At her Karlsruhe Schloßgarten she cultivated both native
and exotic species, and she had paintings and copper engravings made of each specimen for
a planned catalogue of her collection, with the plants arranged according to the Linnaean
system. It was for this purpose that, in 1764, she appointed Koelreuter Director of the
Palace Gardens at Karlsruhe, as well as Professor of Natural History in charge of her exten-
sive natural science collections. Prior to his arrival, Koelreuter published the fourth paper
in the series on the sexual theory, and, with Princess Caroline Louise’s encouragement, he