3 74 i Flora Unveiled
a specific type of mutation in a single gene that controls corolla and stamen development
in flowers with bilateral symmetry, such as Linaria and Antirrhinum (snapdragon).^71 The
population of Peloria that the Uppsala student first stumbled upon was actually reproduc-
ing vegetatively rather than by seed, because such mutants tend to be sterile. The atypical
Peloria inflorescence with the mixture of normal and mutant flowers we now recognize
as an example of the phenomenon of “scattered peloria,” caused by the instability of the
Peloria mutation.
Despite the temporary setback of Peloria, the irrepressible Linnaeus continued to believe
that the number of species was not fixed. New species had arisen since the Creation and
continued to arise through hybridization. After 1745, he dropped the idea of hybridization
among orders, but he was still confident that hybridization could occur between genera and
that this was the source of most new species. Indeed, everywhere Linnaeus and his students
looked in the field, they saw abundant examples of intermediate forms that they interpreted
as hybrids. In the dissertation Plantae Hybridae (1751) published under the name of his
student J. J. Haartman, Linnaeus listed no less than a hundred possible hybrids identified in
natural settings or in botanical gardens. Among these were several putative hybrids between
different genera, including Ve ro n i c a × Verbena, Saponaria × Gentiana, and Aquilegia ×
Fumaria. These three pairs of genera also belong to different families, so their hybridization
is highly unlikely. Linnaeus never tried to generate such intergeneric “hybrids” artificially.
In one case, however, Linnaeus confirmed the authenticity of putative hybrid between
two species that he observed in his garden by creating the identical hybrid in an experi-
ment. In 1760, the Academy of Sciences in St. Petersburg staged a competition for the
best essay demonstrating sex in plants. Linnaeus submitted an essay entitled Disquisitio
de Sexu Plantarum and was awarded the prize. After reviewing the history of the prob-
lem, Linnaeus described some emasculation experiments, similar to those of Camerarius
and Bradley, demonstrating the requirement for pollination for viable seed production.
He then cited the earlier mentioned three unverified “hybrids” as further evidence that
sexual reproduction occurs between different genera. However, he also reported a fourth
hybrid he observed in his garden growing between two species of goatsbeard or salsify,
both members of the Aster family: Tragopogon pratensis and Tragopogon porrifolius. The
following spring, he dusted the stigma of T. porrifolium with pollen from T. p ra te n s e and
collected the resulting seeds. When planted, the seeds gave rise to hybrid plants bearing
“purple flowers, yellow at the base,” similar to the natural hybrids he had observed in his
garden, and the authenticity of this hybrid is generally accepted today. “I doubt whether
any experiment demonstrates the generation of plants more certainly than this,” he con-
cluded with characteristic modesty.
Notes- von Sachs, J. (1906), History of Botany (1530– 1860) trans. H. E. F. Garnsey and I. B. Balfour.
Oxford at the Clarendon Press, p. 391. Originally published in German in 1875. - William Harvey’s The Motion of the Heart and Blood (De Motu Cordis) was published in
Frankfurt in 1628. - Tournefort was not the first to employ the term “genus.” Aristotle used it in some contexts,
as did Cordus (1541), Gesner (1551), and Bauhin (1623). However, as pointed out by Sachs (1875)