Flora Unveiled

416 i Flora Unveiled

Koelreuter’s first success in creating an artificial plant hybrid came in 1760, while he was
still in St. Petersburg. As he wrote in his 1761 paper,

after many experiments instituted in vain with many kinds of plants, I have finally ... in

the case of Nicotiana paniculata and Nicotiana rustica, gotten so far that I have fertilized

with the pollen- dust of the former, the ovary of the other, obtained perfect seeds, and

from these, still in the same year, have raised young plants.

Although the hybrid tobacco plants grew and flowered normally, the pollen produced by
the stamens was dried and shriveled in appearance and there was less of it. Since Koelreuter
did not believe Linnaeus’s Tragopogon hybrid was a true hybrid, and he was unaware that
Fairchild had already created the first plant hybrid decades earlier, he described his own
tobacco hybrid as the “first botanical mule”:

The fertility of this new plant appeared to me, therefore, extremely questionable, and

the results confirmed my suspicion completely; for among the almost innumerable

quantity of flowers there was not one to be found which had borne even a single seed,

even though they had been immediately covered with a large quantity of their own

pollen dust; while on the other hand, with the two natural species, every capsule is

accustomed to bear four to five hundred seeds. This plant is thus in the real sense a true,

and so far as is known to me, the first botanical mule which has been produced by art.

Fairchild and Linnaeus may have produced their artificial hybrids earlier, but Koelreuter
deserves scientific priority because of his thorough documentation, quantitative analysis,
and exhaustive follow- up experiments. For example, the floral organs of Nicotiana rustica
are shorter than those of Nicotiana paniculata. Koelreuter’s measurements of the floral
organs of the hybrid flower showed that they were intermediate between the two parents
(Figure  15.1). This was consistent with Koelreuter’s materialist conceptual framework
regarding the mechanism of inheritance, as discussed next.

Koelreuter’s Theory of Uniform Liquid Essences

Although Koelreuter was refreshingly modern in his scientific methodology, his conceptual
framework was deeply rooted in eighteenth- century philosophy. Not even a hint of evolu-
tionary thinking is to be found in his writings. Whether he was discussing the geographical
distribution of species or the elegant adaptations between flowers and insects, it was always
in terms of a well- designed world and the wisdom of the Creator. A  believer in the fixity
of species, he viewed the sterility of hybrids to be a necessary barrier to prevent “incredible
confusion” in nature. Paradoxically, Koelreuter’s adherence to the fixity of species concept
helped him to avoid Linnaeus’s mistake of assuming that intergeneric crosses occurred with
some regularity in nature. Contra Linnaeus, Koelreuter insisted that species hybrids were
very rare in nature and that intergeneric hybrids were prohibited. Most hybridization, he
argued, occurred in gardens, where related species that normally grow geographically iso-
lated from each other were cultivated in close proximity. This, he explained, was the plan of
the Creator, who, in his wisdom, had distributed closely related species around the world in
order to prevent them from hybridizing.