470 i Flora Unveiled
Schleiden’s Asexualist TheoryMatthias Jacob Schleiden regarded the sexual theory of plants as an egregious example of
scientific anthropomorphizing. As the co- founder and tireless champion of the cell theory,
he argued in 1853 that the entire life cycle of seed plants is based on duplicative cell divisions,
which we now call mitosis, which produces seeds by a vegetative (clonal) process:
the individual vegetable is endowed with the power of forming new cells in its inte-
rior, and thus, as it were, of propagating itself. Now, the newly- formed cells have also
this peculiarity, they grow and arrange themselves conformably to the cell in which
they originate. This is the power given to all plants, to develop new plants out of any
of their cells, when these come to be placed in favorable circumstances, and by this
power is explained the facility with which almost all plants may be multiplied.^18Schleiden cited numerous examples of vegetative propagation, both natural and horti-
cultural, in support of his theory. He repeated, without attribution, Goethe’s interpreta-
tion of leaves, roots, and branches as separate individuals, consistent with the idea that an
individual plant can be thought of as a clonal colony.
Although knowledge that plants are able to regenerate from cuttings can be traced at
least as far back as Aristotle, Schleiden modernized our understanding of the phenome-
non by connecting it to the mitotic divisions of individual cells. Unlike the somatic cells of
Figure 17.4 Stages of sexual reproduction in the life cycle of a typical fern. A. Antheridia, located
among the rhizoids on the underside of the prothallus, produce sperm cells. B. Archegonia, located
near the notch of the heart- shaped prothallus, produce egg cells. C. At maturity, the sperm are
released from the antheridia. D. The sperm cells swim to the archegonia and fertilize the egg. E. The
developing zygote forms roots and juvenile leaves and emerges from the archegonium. Subsequently,
the prothallus undergoes senescence and withers away, leaving a fully independent fern plant.