Sporophyte or gametophyte?
In aroids on Earth, the plants we grow and enjoy are known as the sporophyte in the plant's life cycle.? In fact, all seed plants we see every day are sporophytes!? However, what I visualized as the humanoid-like Aroidian was not a sporophyte; the picture at right illustrates a true Aroidian sporophytic phase.? This particular plant will yield a gynoecious (female) gametophyte, and has a ribbed, melon-like base that develops completely underground.? By contrast, a sporophyte yielding an androecious (male) gametophyte (illustrated at left) develops the bulbous base above ground.? I referred to these melon-like structures as vaginaria (singular, vaginarium) because the mature humanoid-like Aroidians developed within them.? But what did they develop from?? The answer to that question is what makes this phase the sporophytic phase -- they develop from sporoids, analogous to fern spores.
On Earth, the familiar fern plant is the sporophytic phase in the fern life cycle.? Fern spores are produced in spore-bearing bodies called sori, formed on the undersides of the fern fronds.? These spores are haploid, meaning that they have half the normal complement of chromosomes.? When these spores germinate, they produce a tiny haploid plant called a gametophyte.? This gametophyte is so named because it produces gametes, the sperm and egg, which together are the sexual reproductive phase of the plant.? When the gametes join and form a zygote, the result is the diploid fern, a plant with two sets of chromosomes.
On Aroidia, the vaginarium of the Aroidian sporophyte is similar to a giant sorus, within which a single sporoid is produced.? This sporoid is not released, but instead germinates and grows within the vaginarium, forming the gametophyte of the species.? This gametophytic phase is not only haploid but is also dioecious, meaning that androecious (male) gametophytes produce the sperm cells and gynoecious (female) gametophytes produce the egg cells.? Once the fully developed gametophytes emerge from the vaginaria, and sperms and eggs unite, zygotes are formed.? The "seeds," or semmules, are then produced from the zygotes, and from these semmules the sporophytes grow.
So the Aroidians were actually the gametophytes, not sporophytes, and the semmules are what produced the sessile, or stationary, sporophytic phase.? The sporophytes in turn produced the humanoid-like Aroidians, thus completing the life cycle of these unusual entities!? I decided to use the term phytometamorphosis to describe this entire process.
I then understood that the morphological differences seen in the Aroidian sporophytic phase were not due to genetic variability.? Instead, the two differing forms resulted from the effects of hormones produced by the developing gametophytes within the vaginaria.? Being the non-sexual phase, the sporophytes had no hormones of their own with which to induce secondary sexual characteristics.? Therefore, what happened was that the developing gametophytes took over the development of the sporophyte hormonally, altering it to suit their own development.? This is why I observed two different kinds of sporophyte plant.
In the drawing of a young Pinnatidendron at left, three Aroidians in the gametophyte phase can be seen attached on the underside of the leftmost frond.? Their "leaves" are photosynthetic and cannot function as wings.? Instead, the Aroidian uses them to glide between Pinnatidendron plants and for alighting on the ground.? The Aroidian moves not with muscles, as in Earth animals, but via changes in hydrostatic pressure within contractile tubules that serve the same function as muscles.? This hydrostatic activity also results in the "shrinking" of the Aroidian body whenever the glide leaves are fully expanded, in much the same way as a newly emerged butterfly body decreases in size as the immature wings are pumped full of fluid and expanded.? What this means is that when the glide leaves are fully expanded, the Aroidian body is about the size of a chimpanzee on Earth.? When the glide leaves are shrunk back, or retracted, the returning fluids enlarge the body to about the size of an adult human.
(Continued in Part III: What's swimming around down there?)