[Fwd: RE: [Fwd: SPAC]]

lee hadden hadden at wingate.edu
Fri Dec 7 12:21:59 EST 2001


I don't know where to BUY them, but someone in your art / ceramics
department ought to be able to make one.   Just have them fire a porcelain
shape of your design once [I think they call what comes out of that firing
"green ware"].  That ought to be still porous enough [like earthenware
flower pots] to work if you want the evaporator to be ceramic.

Lee Hadden
Wingate University

Jon Monroe wrote:

> -------- Original Message --------
>      Subject: RE: [Fwd: SPAC]
>         Date: 7 Dec 2001 14:20:23 -0000
>         From: drobinson at bellarmine.edu ("Robinson, Dr. David")
> Organization: BIOSCI/MRC Human Genome Mapping Project Resource Centre
>           To: bionet-plants-education at net.bio.net
>   Newsgroups: bionet.plants.education
>
> Katherine:  That Atmometer sounds neat. How thick is the glass tubing I
> wonder? Soil potentiometers have porous ceramic bulbs on them, so maybe
> they could be rigged up.
>
> Wish I could find a place to purchase an Atmometer though. Anyone out
> there know who makes/sells these?
>
> Thanks. Dave Robinson, Bellarmine U.
>
> -----Original Message-----
> From: kschmid at butler.edu [mailto:kschmid at butler.edu]
> Sent: Thursday, December 06, 2001 6:45 PM
> To: plant-ed at net.bio.net
> Subject: RE: [Fwd: SPAC]
>
> I have never tried with a sponge, but we regularly do the analogous demo
>
> with a porous ceramic bulb called an "atmometer."  The atmometer looks
> rather like a hollow button mushroom.  You fit a rubber stopper with a
> long
> piece of glass tubing into the stalk of the mushroom.  The whole
> apparatus
> is filled with distilled water, and the end of the tubing is plunged
> into a
> beaker of a denser liquid while clamps are adjusted to hold the
> apparatus
> bulb end up.  We turn on the "sun" (a flood lamp on a lab stool) so that
> it
> shines on the atmometer bulb, and take periodic measurements of how far
> the
> heavy liquid has been pulled up the tube to replace the water
> evaporated.  I
> am told that in the old days the second liquid was mercury, but I use a
> heavy sugar solution colored with kool-aid for an easily observed
> interface.
> Diffusion of water down into the sugar isn't fast enough to interfere;
> We
> usually get the liquid to be pulled almost all the way up the tube
> (several
> feet) in just over an hour, MUCH faster than movement in a "root
> pressure"
> demo in which water flows into a hollow carrot containing colored KCl
> and
> then moves up an equivalent glass tube.
>
> It helps to boil the atmometer ahead of time in distilled water to
> minimize
> air bubbles, and to handle only the "stem" after this to avoid getting
> greasy fingerprints on the porous part of the bulb.  Needless to say,
> it's
> also important to dismantle things before the sticky colored sugar makes
> it
> into the ceramic.
>
> Does anyone know if these atmometer bulbs are still marketed?  We've
> broken
> a few recently, and I'd hate to lose this demo.  It would be even better
> to
> have enough for students to have races, doing whatever they can with
> lamp
> heat, wind, etc. to speed the flow before a discussion of how guard
> cells
> would respond to such stimuli.  I have also heard that there are/were
> fancier versions of porous ceramic made in the shape of leaves.
>
> _____________________________
> Dr. Katherine M. Schmid
> Dept. of Biological Sciences
> Butler University
> 4600 Sunset Ave.
> Indianapolis IN  46208
> 317-940-9956
> kschmid at butler.edu
>
> -----Original Message-----
> From: drobinson at bellarmine.edu [mailto:drobinson at bellarmine.edu]
> Sent: Wednesday, December 05, 2001 10:43 PM
> To: plant-ed at net.bio.net
> Subject: [Fwd: SPAC]
>
> Does anyone have an easy demonstration to show that the Soil-Plant-Air
> Continuum (the Transpiration-Cohesion Hypothesis) is a legitimate
> concept for explaining how water moves up tall plants?
>
> If you take a long glass tube full of water and sit it in a beaker of
> water with a wet sponge attached at the top will the evaporation of the
> sponge be replenished by water in the glass tube being pulled up, like
> every botany textbook implies?  My first thought is "no".... that the
> column of water would be too thick, and the sponge would evaporate too
> quickly to simulate what might be going on in a plant (in other words, I
>
> think the water column would break)....if I am correct in this
> conclusion, then how CAN you demonstrate empirically that this happens?
>
> The popular Plant Physiology lab books really don't have ways that
> effectively show that the SPAC is "real". I've already seen the labs
> where you cut plant stems underwater (in blue dye) and the dye can be
> observed to being taken up....but that only shows that the xylem is
> under negative pressure...it doesn't show that the negative pressure is
> enough to pull the water all the way to the top of a tall plant.
>
> Just curious if anyone had developed any really cool demonstrations of
> this.
>
> Thanks. Dave Robinson
>
> ---
>
> ---
>
> ---

---




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