coconuts, the thread that won't break!

David Starrett dstarret at BIOLOGY.SEMO.EDU
Sun Aug 29 11:27:10 EST 1999


At 06:21 AM 8/28/99 -0700, PROFDHW at aol.com wrote:
>
>The probable reason for so much confusion about coconuts, aside from
>ignorance (meant in the sense of "uninformed") about plant structure in
>general, is that coconuts are monocots (mono- = one, -cot = cotyledon) and
>most discussions of cotyledons are broached from the dicot (di- = two)
>perspective. This probably relates to the fact that many (Most?) dicots have
>emergent cotyledons while few (if any; Ross? David H.?) monocots use their
>single seed leaf (the other name for a cotyledon) for anything other than as
>an absorptive interface between the endosperm and the growing part of the
>embryo. Emergent, photosynthetic cotyledons are much easier to point to in
>lab.
>
>Even in dicots with hypogean (underground) cotyledons which remain inside the
>seed coat, such as the garden pea (_Pisum_ _sativum_), the cotyledons are
>easy to demonstrate. Try this with the monocot corn (_Zea_ _mays_).

The cotyeldon in corn is easy to find.  I have students dissect soaked corn
kernals, they can easily locate the cotyledon (scutellum).  It is the
sliver like structure we pick from our teeth.  It serves to soak up the
nutrients from the endosperm and transfer them to the developing embryo
proper (the cotyledon is most certainly embryo, simply following plant
development one can see the cotyledons develope from the embryo.  In
dicots, the wings on heart-shaped stage, etc.)

My original question was where in a coconut is the cotyledon?  Is it
similar to corn in being small transfer site, is it really not there much
at all, or is another structure in this somewhat unique seed the equivalent
of the cotyledon?


Dave


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