From our present perspective, we'd find it weird, to say the least, that we looked similar to our grandparents and our grandchildren, but our parents and our children looked like something recently arrived from Mars. Yet, that's what we see in plants. Ferns alternate the familiar form that we envision as ferns with tiny plants unrecognizable to us as ferns. Our everyday plant, like ourselves, has two sets of chromosomes in each cell. The children of that fern, though, not only look different, but have only one set of chromosomes per cell. Those minute offspring produce eggs and sperm that fuse to grow up to be our familiar, frilly ferns.
Our beloved flowering plants have adapted this pattern. They have the
two sets of chromosomes, but tucked away in the flowers, they produce tiny offspring
with single sets. One, which we know as pollen, produces sperm. The other, hidden
within the female parts of the flower, produces an egg. Bring the two members of that
generation together, and the result? A seed! Strange, strange, strange!
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.