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Cryptocoryne Roots

  • Subject: Cryptocoryne Roots
  • From: Ted.Held@hstna.com
  • Date: Thu, 27 Jun 2002 11:26:03 -0500 (CDT)


I think my first posting of this message got snagged somewhere. I apologize
if it shows up twice.


Prompted by the recent discussions about water roots and terrestrial roots,
I decided to have a close look at the root of a Cryptocoryne griffithi
under a scanning electron microscope (SEM). I was able to secure four
excellent SEM photos of the outer surface of the root. For those unfamiliar
with Cryptocoryne, this genus of aroids grows in very wet environments and
submerged in water. As a consequence their roots are presumably geared to
soggy conditions. Cryptocoryne are grown by aquarium people because they
are decorative.

The query I have for the list is to explain an unusual (to me) morphology
that I found on the root surfaces. The basic root skin is a regular array
of close-packed cells, whose individual surfaces are quite smooth.
Cryptocoryne (at least C. griffithi) do not seem to have any root hairs.
Occasionally there will be a branch. But otherwise the root surface is
rather boring. The cells are uniform in size and packed in neat rows like
bricks, with each row offset by a half a cell from its neighbor.

The curious structure, the subject of my query, is what appears to be a
filmy membrane, loosely encasing the root skin. The membrane is structured
as a thin film stretched between what look like rope boundaries. The ropes
form a regular pattern almost exactly conforming to the underlying cell
rows. The ropes seem to create an open network analogous in size and shape
to the cells with the loosely stretched membrane between (and below, so
that the membrane rests on the cell rows and the ropes above). The net-like
rope support structure seems to favor running along the middle of each cell
in the skin so that the appearance is very geometrical.

On an older section of root, the cells are slightly smaller and the
membrane ropes thinner. On a younger root section, the ropes give the root
a shaggy appearance under high magnification.

The cross sectional interior cells of another Cryptocoryne (C. usteriana)
reveals that the skin cells are the smallest cells in the root. The
interior cells vary in size and placement and have no evident organization
beyond a small "pith" in the center.

I realize that a written description is no substitute for actually viewing
the picture. For those who might need a picture to offer an informed
opinion and to others who may be simply interested in seeing an SEM, I can
send any or all these pictures to them via private e-mail. Just contact me
at: ted.held@hstna.com. I have four SEM pictures currently, as follows, all
of the C. griffithi. All SEMs are black and white unless artificially
colored.

1. Older viable root, 140X, showing the overall patterns of the cell rows.
2. Older viable root, 1000X showing a detail of the same setion with the
membrane structure.
3. Middle aged (younger) root, 140X, showing a more elongated cell pattern
than #1 and which shows the rougher surface by the more pronounced rope
structures along the surface.
4. Middle aged root, 1000X, a detail of #3, where the rope and membrane is
most easily seen. This is the picture I used for my descriptions.

I realize that what I have seen is from a single species and that it may
not be representative. I do have intentions of looking at other
Cryptocoryne (and other aroids) but this is something I sneak in at odd
times and the process is rather time consuming. Do any others on the list
have access to an SEM? I think a survey of root morphologies in aroids
would be very interesting and perhaps germain to the discussions of
water-adapted roots.

I warn any takers that each of these picture files is a meg in size (big)
and may take a while to download, depending on your internet service. But
the detail is quite good. In picture #2, for example, several diatoms are
clearly visible, nestling among the cell boundaries. Under an ordinary
microscope without staining the cells are too transparent to see many
details.

I'd appreciate any comments on the membranes from those familiar with
botany.





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