I am a physiologist rather than an evolutionary scientist so I don't know
if I am on firm ground. The loss of a cotyledon to go from monocot to
dicot might be related to their usually hypogeous germination. In corn,
the cotyledon remains inside the seed and functions in absorption rather
than being carried above the ground (epigeous) and functioning in
photosynthesis. Bean is rather atypical in this regard because the
cotyledons are not as leaflike as in most common dicots. Of course quite a
few dicots are also hypogeous.
The difference in leaf venation between monocots and dicots is also usually
stressed. The so-called parallel venation of monocots seems a necessity for
leaves which elongate from their bases, like amaryllis and grasses. The
advantage to the plant is that the meristem is protected from grazing by
being located low to the ground or underground.
******************************************************************
David R. Hershey
Snail mail: 6700 Belcrest Road #112, Hyattsville, MD 20782-1340
Adjunct Professor, Biology/Horticulture Department
Prince George's Community College, Largo, MD 20772-2199
Email: dh321 at pgstumail.pg.cc.md.us
*******************************************************************
On 15 Nov 1996, Jon Monroe wrote:
> Plant-ed:
>> I'm posting this message for Jim Bader at Case Western Reserve University.
> He posted it yesterday on the Biolab list. In addition to replying to
> Plant-ed, please forward your replies to Jim at: jxb14 at po.cwru.edu>> Thanks, Jon
>> >Biolabbers
> >We have just finished our week on plant diversity in which we looked at
> >evolutionary advances in reproductive structures from mosses to ferns to
> >gymnosperms to angiosperms. While discussing the structure of monocot
> >(corn) and dicot (kidney bean) seeds, one student asked what the
> >evolutionary significance of these differences might be. While I could
> >supply information on different lineages within the angiosperms and
> >developmental and morphological differences between monocots and dicots, I
> >was hard pressed to account for the evolutionary forces that may have lead
> >to the development of these lines.
> >
> >Am I overlooking the obvious? Is there a simple answer that escaped me
> >since we are buried under four feet of snow, it is not even Thanksgiving,
> >and we are nearing the end of the semester with our tails between our legs?
> >
> >James M. Bader
> >Manager of Graduate and Undergraduate Biology Teaching Laboratories
> >Assistant Director, Center for Biology Education
> >Case Western Reserve University
> >jxb14 at po.cwru.edu>>>> -----------------------------------------------------------------
> Jonathan Monroe voice: 540-568-6649 (office)
> Department of Biology 540-568-6045 (lab)
> James Madison University fax: 540-568-3333
> Harrisonburg, VA 22807-0001 e-mail: monroejd at jmu.edu>http://www.jmu.edu/biology/biofac/jmonroe/jmonroe.html> -----------------------------------------------------------------
>>>
