372 i Flora Unveiled
difference in the flowers no one can recognize the plant anymore. This is certainly no
less remarkable than if a cow were to give birth to a calf with a wolf ’s head.^64To avert such a taxonomic catastrophe, Linnaeus concocted an alternative hypothesis
that would save his classification system. Linnaeus argued that Peloria must be a hybrid
between Linaria and some unidentified, but markedly different, plant. Hybridization was
infinitely preferable to “transmutation” because it left his classification system more or less
intact. In his correspondence with Johann Georg Gmelin of Tűbingen, Camerarius’s old
mentor, Gmelin shared anecdotal evidence that Delphinium could give rise to new types of
plants when hybridized with other genera, thus supporting Linnaeus’s hypothesis.^65 A new
theory of the origin of species based on hybridization began to crystallize in Linnaeus’s
mind. One just needed to understand how hybridization worked. Linnaeus believed his
medulla– cortex theory provided the answer.
Nicolaus of Damascus in De Plantis had distinguished between the tissues of the outer
cortex of plant stems and those of the medulla, or pith. Cesalpino, Malpighi, and Grew
had all embraced the idea that the cortex was responsible for nutrition and the production
of leaves, while the pith, or “womb,” gave rise to the seed. In his treatise Metamorphosis
Plantarum (1755), Linnaeus elaborated the medulla– cortex idea still further. According to
Linnaeus, pistils arose from the medulla, indicating that the medulla is female. Stamens, on
the other hand, were extensions of the cortex, so the cortex must be male. The male cortex,
according to Linnaeus, functions mainly in nutrition, whereas the female medulla repre-
sents the life force of the plant, manifesting a kind of will to reproduce.^66
During fertilization, the male pollen gives rise to the cortical tissues of the embryo, while
the female ovule produces the medulla.^67 Because the female medulla gives rise to the seed
Figure 13.2 The toadflax Linaria vulgaris with bilateral symmetry (left) and the radially
symmetrical peloria mutant (right).
From Busch, A., and S. Zachgo (2009), Flower symmetry evolution: towards understanding the abominable
mystery of angiosperm radiation. BioEssays 31:1181– 1190.