I did the "negative" thing with my class a few years ago.
I used a digital camera, tweaked the photos for higher
contrast using photoshop, inverted them to negative, and
printed them onto transparency stock in the laser printer.
These made nice big negatives for the project. We got
some leaves with FANTASTIC results. Some were barely-passing.
I too had permanence problems. I think the volatility of
iodine plays a role in that. There are some other stains
that will color starch...a purple one I recall from
grad-school days...but I don't remember what it was now,
and I am ashamed to say I never bought a copy of Sass...
If you do find out what other dyes work for starch, I'd
love to know.
At 4:48 PM +0000 3/13/00, Jon Monroe wrote:
>Beverly et al.,
>>The book by Carol Reiss, "Experiments in Plant Physiology" has a
>number of good exercises that could be adapted for first year bio
>courses. One of them that I tried for the first time this semester
>in Plant Phys involves taking photographs of the students (probably
>not feasible for big intro courses), then taping the negative to a
>bean leaf that was depleted of starch, exposing the leaf to light
>then clearing the leaf and staining with iodine. When it works it
>is spectacular but we had troubles getting good prints.
>>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?
>>>Does anyone have a photosynthesis lab of which they are particularly
>>proud? We have two labs, one for non-majors and one for majors. They
>>include variations on watching spinach disks rise in varying light
>>intensities, varying wavelength intensities, and the old Coleus leaf,
>>boiled, with iodine, etc. This series of experiments is prone to great
>>failure and we would like to revamp it entirely!
>>>>Beverly J. Brown, Ph.D. Phone: 716-389-2555
>>Nazareth College of Rochester Fax: 716-586-2452
>>Biology Department E-mail: bjbrown at naz.edu>>4245 East Avenue
>>Rochester, NY 14618-3790
> 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>http://csm.jmu.edu/biology/monroejd/jmonroe.html>--------------------------------------------------------
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Biology Department | http://koning.ecsu.ctstateu.edu/
Eastern CT State University | phone: 860-465-5327
Willimantic, CT 06226 USA | fax: 860-465-4479
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