26 May 2003 22:22:38 -0700 galathaea wrote:
(mine snipped)


Most definitely. We always start grasping and fine tune only later.


Question: Why should any plant have its first two leaves very much different from all other successive
leaves? That is the question that is bothering me. Why
should my baby pear tree have its first two leaves so starkly different from
its future leaves. Do these first leaves confer some superior advantage to the plant
or are they different because of the ancient past of the species, the genetic mess
of the species is brought forth in its first leaves.

What I had tried to convey in my first post was the variability of
forms in the cotyledon. This is strong evidence to point to the fact
that they have been an active part of evolution and are not mere
vestiges. They have a purpose separate from those of the mature
leaves of the plant: although they too participate somewhat in
photosynthesis, they are in reality a part of the seed mass and store
starch and other materials to assist in getting the plant growth
started. Making comparisons between cotyledons and mature leaves
would not be beneficial; they are separate organs with separate jobs.

I believe it is a question of whether genetic-mess (like gill slits in humans) or
whether these first leaves confer some survival advantage on the seed growing
to maturity.

My guess is that it is "genetic mess of the past". And that if the plant had a choice of having its
first leaves such as a pear tree, that the plant would have
all of its leaves of one type. That the true pear leaf is superior in every way
such as photosynthesis ability than the cotyledon first leaf.

The reason's cotyledons may not appear in certain plants is because
other seed mass may be sufficient for those plants in the environments
in which they have adapted. Other plants rely heavily on the
cotyledons for their immediate readiness to participate in assisting
the plant's early growth, and photosynthesis, transpiration, and other
tasks normally assigned to leaves may be done by the cotyledons after
first emergence from the soil.

So, basically, what I am trying to show is that the cotyledons should
be seen more as separate organs than as early developmental forms.
They have evolved quite alot and take many forms, and I do not believe
it would be proper either genetically or by form to characterize them
as evolutionary vestiges.

But I do enjoy the question. It is certainly a valid line of
reasoning, and fortunately there is alot known about these fascinating
little cotyledons to provide a fairly good answer. Unfortunately, I
think the answer is most likely negative...

Thanks for answering the question with clarity.

Which leads me to a different line of questioning-- as always in science,
it never ends but leads into new routes and viaducts.

My pinenuts and potatoes do not seem to have cotyledons. So I am guessing
that only plants whose seed is insufficient in energy (ie mass) must have
some cotyledon structure in order for the plant to have enough energy to
reach the noncotyledon-Leaf stage. A pinenut has sufficient energy reserves
that its first leaves are identical to all later leaves and same goes for the
potato. May have that wrong but if correct would suggest that Size of seed
as per mass is directly related to whether a cotyledon must exist or not. The
tomato seed is puny in size and so must have a large cotyledon.

Question for Galathaea if not bored: Has there been a research done on the
size of seed (mass) correlated to whether the plant has or has not a cotyledon
and whether at a particular mass all plants of a greater mass have no cotyledon
(potato, pinenut etc). My pear tree had a cotyledon and its seed is small same
with strawberry seeds but a coconut or nut trees may not have cotyledon?
Is there any correlation between size of seed per mass and whether it has
a cotyledon or not?

P.S. in my earlier post I was asking whether some method exists that tells
us how much photosynthesis is going on per square area of a cotyledon leaf
compared to a mature leaf. In light of the new understanding above that a
cotyledon is a different "organ" so to speak, perhaps we can use cotyledons
as a gauge.

Archimedes Plutonium,
whole entire Universe is just one big atom where dots
of the electron-dot-cloud are galaxies