I don't want to belabor the original Ginkgo question, but recent posts
on the seed have raised my curiosity about the life cycle.
Scott Shumway has asked what to call the "thing" (my word, not his) that
falls from the Ginkgo tree and that ultimately contains the embryo. It
was an ovule on the tree, containing a single megaspore, so it is still an
ovule on the ground, soon to become a seed after it finally gets
fertilized. But this raises a new question in my mind. Does the ovule
continue to increase in size after it falls? If so, how large is it when
it falls? At what point do we start calling it a seed? Are ovules with
fertilized eggs considered seeds as soon as they are fertilized, or not
until they are mature and, in most cases, ready to leave the fruit or
parent?
My Biology Dictionary (Harper Collins) defines a seed as "the structure
IN an ovule that ...," then closes with including the integuments as part
of a seed. Am I missing something? How can it be "in" an ovule?
Raven, Eichert, and Eichorn in Biology of Plants define seed as "a
structure formed by the maturation of the ovule of seed plants following
fertilization." That was always the concept I had understood, but in
Ginkgo, how does one know when that has occurred?
Are there any other plants that are fertilized after the seed leaves the
parent plant (as a normal occurrence).
Thanks,
Janice
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Janice M. Glime, Professor
Department of Biological Sciences
Michigan Technological University
Houghton, MI 49931-1295
jmglime at mtu.edu
906-487-2546
FAX 906-487-3167
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