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photosynthesis lab

Jon Monroe monroejd at jmu.edu
Tue Mar 14 22:21:29 EST 2000

Nancy Harrison wrote:

>On 13 Mar 2000 16:48:48 -0000, monroejd at jmu.edu (Jon Monroe) wrote:
>>For my daughter's 4th grade class a few weeks ago we did this but
>>instead of using negatives they cut out shapes from black paper and
>>paper-clipped them to the leaves.  After staining the contrast
>>between shaded and lighted parts of the leaf was wonderful :-) but
>>after pressing the leaves in paper towels over night all of the
>>iodine stain disappeared. :-(  Does anyone know why this happened and
>>how to prevent it?
>Jon: We do this experiment with geranium leaves - using foil
>with crosses cut out (same idea). The leaves with and without
>masks are boiled in alcohol to remove pigment, then placed
>in petri dishes with Iodine solution. After everyone has observed
>and sketched the leaves, we pour off the I2KI soln, cover
>the dishes, and place in our specimen frig. They keep fine,
>with stain intact, for several months! -

So if you don't wash the leaves in water or dry them, then apparently 
the iodine stays there...

>  Maybe it's the boiling in alcohol that helps them keep - you
>might not have wanted to do this in a 4th grade class! - NH

Well I did.  I was doing the dipping...   The other trouble we had 
when I did this with my Plant Phys class was that the leaves tended 
to fold up in the ethanol and were difficult to spread out flat.  I 
had the 4th graders use time tape to fix the leaves to tin foil and 
it turned out to be really easy to go through the boiling water, 
boiling ethanol and iodine stain.  Carol - put that into your next 

The kids also painted fingernail polish of various leaves and got 
some nice views of epidermal cells.  I was amazed with the ones on 
spider plants!  Beautiful.

Thanks all.


>Nancy Harrison
>T.A.Botany at Santa Rosa Jr.College
>Milo Baker Chapter, California Native Plant Society

  Jonathan D. Monroe           	    Associate Professor
  Department of Biology, MSC 7801   office: 540-568-6649
  James Madison University	      fax: 540-568-3333
  Harrisonburg, VA 22807   	email: monroejd at jmu.edu

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