494 i Flora Unveiled
or megaspore. The megaspore then divides mitotically to form a new haploid plant— the
embryo sac. Thus, the ovary, like the anther, is an asexual, spore- producing structure.
Although stamens and pistils are asexual structures, it is also true that they specifi-
cally give rise to the male and female gametophyte generations, respectively. It is thus
convenient to assign these two asexual organs different genders: stamens are gendered
male and pistils are gendered female. In adopting this convention, we are following
the lead of Beukeboom and Perrin, who applied the term “gender” (normally defined
as a culturally derived construction) to sporophytic structures that are specialized in
“one or the other sexual function.”^27 Although this practice risks a certain amount of
confusion, which we are trying mightily to avoid, such a plant- specific definition of
gender makes it easier to talk about the roles of stamens and pistils in the sexual cycle
of angiosperms.
The two gametophytes, the pollen grain and embryo sac, are genetically distinct from the
sporophyte that produced them, and not only because they are haploid instead of diploid.
As noted earlier, since meiosis involves some exchange of alleles (gene variants) between
chromosomes, new combinations and arrangements of maternal and paternal genes are gen-
erated. This makes the two gametophytes genetically distinct from the sporophyte, which is
why they are referred to as the gametophyte generation. Despite their microscopic size, these
two genetically distinct haploid individuals (male and female gametophytes) are the mature
sexual stages of the plant life cycle.
Like the key to Frances Hogdson Burnett’s Secret Garden, the key to the plant life cycle
was “buried deep,” not in the ground, but in the sporophytic tissues of the flower. Rather
than germinate on soil as the spores of cryptogams do, angiosperm spores are retained
within the two floral organs, stamens and pistils, where they develop into highly reduced
male and female gematophytes. These two types of gametophytes growing inside the anther
and ovary are, in a sense, Flora’s “secret gardens.” The pollen grain, or male gametophyte,
became adapted over millions of years of evolution to hitch rides with wind, insects, or
other animals and land with remarkable efficiency on the surface of the tiny stigma. There
it sprouts a thread- like pollen tube that grows down through the style and forms a conduit
for the accurate delivery of two sperm cells to the embryo sac, or female gametophyte. The
fusion of sperm and egg marks the beginning of the new sporpophytic, or asexual stage, of
the plant life cycle.
For centuries, Flora’s sexuality was concealed under a veil of sporophytic tissue.
Hofmeister’s discovery that seed plants, like the cryptogams, consist of two “generations,”
an asexual diploid individual and two sexual haploid individuals, effectively lifted the veil
of secrecy.
Because of the alternation of generations, the sexualists and the asexualists can both
claim to have been right. However, the asexualists’ position was based on ancient traditions
and social constructions about gender rather than on science. It was the sexualists who suc-
cessfully freed their minds from such cultural biases and glimpsed the true sexual nature of
plants. The sexualists went on to demonstrate the presence of both the sexual and asexual
generations in the life cycles of all plants, as revealed by Hofmeister’s great synthesis, thus
enabling the asexualists to share in the ultimate solution to the puzzle.