Plant-eders,
I'm no expert on this topic, but I picked up my copy of _The
Evolutionary Biology of Plants_ by Karl Niklas (1997, U of Chicago
Press) this morning and found a lengthy discussion relevant to this
thread. I admit that I skimmed it but I think the main point is
this. He argues that land plants took either of two largely mutually
exclusive routes of evolution - amplification of the size of the
gametophyte or of the sporophyte. Gametophyte growth was generally
horizontal because of the need to remain close to water for gamete
movement. Sporophytes that *could* grow vertically (those with
vascular tissue) did so for the advantage of spore dispersal by wind.
I'll stop here and ask others with more background in this field to
read on and explain for the rest of us.
Jon
>Dana Ann Dudle wrote:
> >
>> 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!)
>>>> Thanks,
>> Dana
>> *********************************
>> Dana A. Dudle
>> Dept. of Biological Sciences
>> DePauw University
>> Greencastle, IN 46135
>>ddudle at depauw.edu>> *********************************
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Jonathan D. Monroe Associate Professor
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MSC 7801 lab: 540-568-6045
James Madison University fax: 540-568-3333
Harrisonburg, VA 22807 email: monroejd at jmu.eduhttp://csm.jmu.edu/biology/monroejd/jmonroe.html
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