Steam Girdling

[Janice M. Glime]

Oops!  Now I understand how my students come up with such outrageous
answers on their tests!  I meant killing phloem, not xylem.  Of course I
know xylem is dead.  This communication has been a good lesson to me in
understanding how my students go wrong.  My second error here is in
visualizing a woody stem and not understanding why the stem should need
support after it had been steamed.  It all makes sense when I visualize a
non-woody stem!  It does one good to be a student again, but it can be a
humbling and embarrassing experience!  The polite answers to my questions
below are a good lesson in how to handle such wrong visualizations and
careless fingers!  Thank you, "rodaway."
Janice
***********************************
 Janice M. Glime, Professor  
 Department of Biological Sciences
 Michigan Technological University
 Houghton, MI 49931-1295
 jmglime at mtu.edu
 906-487-2546
 FAX 906-487-3167 
***********************************

 > > Janice, >      
>      The supposition is that the xylem is already non-living conductive 
>      tissue and that the phloem, cortex and outer layers are being killed 
>      by the steam.  You should not be cooking the xylem which might cause 
>      cavitation (a discontinuous bulk water phase). When you apply a 
>      substance via the root and compare movement in girdled vs. non-girdled 
>      shoots you can evaluate whether the substance requires intact phloem 
>      tissue (steam-sensitive tissue) for transport.  Same with applications 
>      via the leaf.  It is a very simplistic method and therefore may 
>      overlook several physiological details.  Support of the stem is only 
>      necessary when the xylem is not sufficiently lignified to act like 
>      stiff "pipes" instead of bundles of flexible tubing.  Eliminating the 
>      turgidity at the girdle may allow the young plant to flop over at the 
>      girdle.
> 
> 
> ______________________________ Reply Separator _________________________________
> Subject: Re: Steam Girdling
> Author:  jmglime at mtu.edu at GATEWAY
> Date:    6/12/98 11:06 AM
> 
> 
>   I'm missing part of this story.  I understand how to examine xylem
> conduction (although new ideas would be welcome), but how do you show the 
> loss of phloem conduction after killing the xylem?  And why does the stem 
> need support after killing it?  Does this have anything to do with living 
> parenchyma cells providing water as water tension builds during the day 
> (ala Canny's recent papers)?
> Thanks.
> Janice
> ***********************************
>  Janice M. Glime, Professor
>  Department of Biological Sciences
>  Michigan Technological University
>  Houghton, MI 49931-1295
>  jmglime at mtu.edu
>  906-487-2546
>  FAX 906-487-3167
> ***********************************
>