What's the point of a triploid tissue?

David R. Hershey dh321 at PGSTUMAIL.PG.CC.MD.US
Thu Feb 27 15:16:49 EST 1997

Biology texts tend to neglect a discussion of gymnosperm seeds, which 
have a haploid nutritive tissue, which is also sometimes referred to as 
endosperm. One text noted that double fertilization provided large food 
reserves in seeds, yet many angiosperm seeds are smaller than some 
gymnosperm seeds. 

Perhaps there is some difference in nutritional content between seed 
storage tissue of gymnosperms and angiosperms?

Biology texts also tend to oversimplify when comparing angiosperms and 
gymnosperms by attributing angiosperm dominance mainly to flowers which 
provide more reliable animal pollination and a fruit to aid in seed 
dispersal and protection. However, there are very successful wind-pollinated 
angiosperms and many other physiological and structural differences 
between angiosperms and gymnosperms that may give an edge to angiosperms, 
e.g. annual and biennial habit, aquatic habit, bulbs, vessels, C-4 
photosynthesis, endomycorrhizae, intercalary meristems, etc.

David Hershey
Prince George's Community College

On 27 Feb 1997, John Hewitson wrote:

> Dear Plant-eds,
> My students ask "What's the point of a triploid tissue?"
> The thinking goes like this:-
> * Triploid tissue is unique to angiosperms.  True?
> * Natural selection does not support a structure unless it confers some
> advantage.  Agreed?
> * The fact that triploid tissue exists suggests that there is some
> advantage.  What is the advantage of a TRIPLOID endosperm?
> * Does a study of angiosperms suggest that the most recent members use this
> tissue less, OR do they make greater use?  What is the direction that
> evolution seems to be taking?
> What do you think?
> Or am I not looking in the right books or surfing the right URLs? (-:
> John
>  _________________________________________________________________
> | Dr. John Hewitson                                               |
> | Berrystead Barn                   +44 (0)1832 272 209 phone/fax |
> | Oundle,                                                         |
> | Peterborough, PE8 4DY, UK.  e-mail John_Hewitson at compuserve.com |
> |_________________________________________________________________|
> (Oundle School:  www.oundleit.demon.co.uk)

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