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)
>
