Dana Ann Dudle
ddudle at INDIANA.EDU
Mon Oct 4 17:40:58 EST 1999
I am constantly amazed at how much we don't know about what seem to be
major transistions! I think having students teach is one of the best ways
to get them to think intensely about a topic.
On Mon, 4 Oct 1999, James W. Perry wrote:
> Two theories to my recollection:
> 1. Homologous (transformation)
> Gpt primitive, spt. of secondary origin, a modified gpt - the gpt
> became "transfomed"
> 2. Antithetic (interpolation)
> Gpt of lower plants is of algal origin
> Delay in meiosis resulted in a spt present in Silurian plants
> Spt eventually became nutritionally independent
> Vegetative tissue arose from sterilization of sporogenous tissue
> No observable evidence exists to my recollection.
> Nothing quite like teaching causes one to ask questions. Maybe we should
> ask our students to do a little teaching if this is the result.
> At 03:12 PM 10/1/99 +0000, Dana Ann Dudle wrote:
> >Hi All--
> >After such helpful and interesting responses to my question regarding
> >polyploidy, I have decided to try yet another question on y'all:
> >What were the intermediate steps between the dominant, photosynthetic
> >gametophyte and reduced sporophyte present in the non-vascular plants
> >(bryophytes), and the dominant sporophyte that is present in all vascular
> >plants (as far as I have been able to discern). The oldest fossils of
> >vascular plants that are most often referenced in textbooks and review
> >articles, e.g. Cooksonia and Rhynia, are called sporophytes...
> >IT seems as if this was a very important development in the evolution of
> >plants, and yet I have found very little reference as to HOW this change
> >occurred. Does anyone know of fossil evidence or living transitional
> >forms that may give some insight into this major change in the focus of
> >the alternation- of- generations in land plants?
> >I have always been taught that "mosses have dominant gametophytes, and
> >ferns have dominant sporophytes", but I have not questioned the "how or
> >why" until I started writing lectures and preparing classes on this topic.
> >Any hints or leads would be greatly appreciated (as well as speculations!)
> >Dana A. Dudle
> >Dept. of Biological Sciences
> >DePauw University
> >Greencastle, IN 46135
> >ddudle at depauw.edu
> James. W. Perry, CEO/Campus Dean
> Professor, Department of Biological Sciences
> University of Wisconsin - Fox Valley
> 1478 Midway Road
> Menasha, Wisconsin 54952-1297
> Office: 920.832.2610
> FAX: 920.832.2674
> jperry at uwc.edu
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