468 i Flora Unveiled
Hedwig correctly surmised, grew and gave rise to the stalk and capsule that later emerged
from the archegonium.^13
Hedwig’s pioneering observations, published between 1782 and 1784,^14 confirmed that
mosses did, indeed, have a sexual stage in their life cycle, even though these sexual struc-
tures were invisible to the naked eye. After many years of studying the life histories of a wide
selection of bryophytes, Hedwig concluded that the two other groups of bryophytes (liver-
worts and hornworts) both had the same general life cycle as the mosses, including “hidden”
male and female sexual organs present on the diminutive structure that developed directly
from the spore. Linnaeus, who had died four years earlier, would no doubt have exclaimed
with vexation, “Vad var det jag sa?” (“What did I tell you?”).^15 Following Hedwig’s discovery
of sex in bryophytes, more than sixty years were to elapse before the basic features of the fern
life cycle were elucidated.
It had long been known that fern spores are typically produced on the underside of fern
leaves (Figure 17.3). The sporangia of fern leaves are bunched together in clusters called sori
(si n g u l a r, sorus). At maturity, the tiny sporangia spring open and fling their powdery spores
some distance away onto the ground where they germinate to produce a short multicel-
lular filament, also called a protonema. When the protonema reaches a certain length, the
growing tip begins to expand laterally resulting in a small, flat, structure about the size of a
quarter. In modern terminology this structure is called a prothallus.
At first, the prothallus was thought to represent the direct precursor of the fern embryo
and was therefore referred to as a “pro- embryo.” Then, in 1844, the Swiss botanist Karl
von Nägeli made the startling discovery of antheridia (microscopic male sexual organs)
on the underside of the so- called “proembryo” (Figure 17.4). These antheridia, similar to
those of mosses, released “spiral filaments,” which were in fact motile sperm cells. This
made absolutely no sense to botanists at the time. Unlike the diminutive mosses, ferns
were comparable in size to seed plants. In seed plants, sexual reproduction was assumed to
be the exclusive function of the adult vegetative plant. It was as if the sexually mature stage
of human beings was discovered to be not the fully grown adult, but the embryonic fetus!
Botanists began to suspect that there was something very unusual about the so- called
“pro- embryo” of ferns. If it was not an early stage of embryo development, what was it?
Although Nägeli had detected antheridia on the undersides of these weird “pro- embryos,”
he was unable to find any archegonia, so the question of the sexuality of these baffling little
plants remained unresolved.
The problem languished for several years, until 1848, when the Polish Count Michael
Jerome Lesczyc- Sumińsky, a young, amateur botanist and illustrator working in Berlin,
took a closer look under the microscope. Voila! He discovered the missing archegonia clus-
tered just above the antheridia on the underside of the so- called “pro- embryo” (see Figure
17.4). The following year, Sumińsky also reported that he saw “spiral filaments” (sperm cells)
exit the antheridia, enter the canal- like neck of the archegonium, and ultimately fuse with a
large cell at the bottom of the canal, which he called the “ovule” or egg.^16 Subsequently, the
fertilized egg divided to form the true embryo, which emerged from what we now call the
prothallus and grew into the mature fern plant (see Figure 17.4).
Although Sumińsky’s astute observations helped to clarify the fern life cycle, they were
peremptorily dismissed by dyed- in- the- wool asexualists such as Schleiden, who regarded
Sumińsky as a rank amateur. He declared that a