One of the major events that occurred concurrent with sporophyte
dominance was the introduction of lignin into plant chemistry. With this
new means of support, sporophytes were able to support the weight of a
larger plant. What intrigues me is that this seems to be expressed only
in the 2n (or greater) plant and never in the 1n plant. In Psilotum,
individuals that have formed 2n gametophytes (at least they look like
gametophytes and produce sex organs like one) have developed some vascular
tissue. What is it about 2 sets of chromosomes that makes this possible
when one set cannot do it?
Then there is Anthoceros, which might be a reduced fern, albeit probably
from an early branch. Its DNA seems to be different from that of other
bryophytes. I don't have this sort of data at my finger tips, but new DNA
cladistics are causing us to ponder.
I could spend more time discussing the antithetic and homology theories,
but must move on to other things.
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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