Dackweed (Stomata)

Ross Koning Koning at ECSUC.CTSTATEU.EDU
Wed Aug 7 10:25:18 EST 1996


At  5:48 PM 7/21/96 +0100, Shaun Carl Whyte wrote:

>Just a quick question, I am doing my A-Level Biology coursework and I
>just need to know one thing really urgently, so I thought I'd try here,
>does the stomata on Dackweed grow at the top or bottom of it?

Shaun,

I just got back from my vacation and found your question
in my email and no reply from anyone...I hope someone
on the net wrote to you directly.

In any case, here is a tardy reply...

I do not know the answer to your question, though I would
take a guess that they are in the upper epidermis.  Here
is how you can determine the answer.  Bring water in a
glass beaker or other pyrex (borosilicate) glass container
to almost (but not quite) boiling water.  Then with fine
forceps, grasp the Lemna (duckweed) plant by its roots.
Plunge and hold the plant under the hot water and observe
through the glass whether bubbles appear on the two surfaces
of the "fronds."  If you remember your chemistry PV=nRT so
the heated gas between cells expands with the heat and
escapes through stomata...the side with the most and largest
bubbles is the side with the most stomata.  A more direct
way to determine this is to use colorless fingernail polish
to "paint" the surfaces.  This film can be peeled off with fine
forceps and observed with a microscope to see the stomatal
impressions.  You could also "clear" the fronds themselves
(maybe in 5% NaOH...CAUSTIC!) and observe directly using
"optical sectioning" to determine which epidermis has the
most stomata.  Of course you can estimate the stomatal density
by counting stomata per field of the microscope at a particular
magnification.

Whatever method you choose, let me know if you have additional
questions or difficulty...my email address appears below...

ross

______________________________________________________________
                            |
Ross Koning                 | Koning at ecsu.ctstateu.edu
Biology Department          | http://koning.ecsu.ctstateu.edu/
Eastern CT State University | Phone: 860-465-5327
Willimantic, CT  06226  USA | Fax: 860-465-5213
____________________________|_________________________________

                Plant Physiology is Phun!

 /\|___/\     //\______COOH   NH-CH2-CH=C-CH2OH  \/OH
|  |  |  |    |  |  ||       //\___     \CH3     /\|/\\/\\COOH
 \/ \/|\/|    \\/ \ /       N  ||  N            |  |
 /\ | |__|=        NH       |  || ||           //\//\
  | COOH                    \\ /\ /            O
  COOH        H2C=CH2         N  NH
______________________________________________________________





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