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Re: HYB: Pigments 101


In a message dated 11/26/00 6:28:00 AM Mountain Standard Time, 
charmike1@juno.com writes:

<< 
 How is this modified (?) or whatever when people report varying hues or
 tints of the same iris in different regions and/or soils? I really am
 only partially awake folks but I've been wanting to ask that question for
 several days now!  >>

Ahhh....   So we want to talk "nature vs. nurture" now?   It helps to think 
of genetics as defining the potential, environment as influencing its actual 
expression, and observers as affecting the reporting/analysis/conclusions.  

Let's start with the Photo Factor -- no film accurately captures all colors 
and further distortion usually occurs during the printing process.  A report 
that "It doesn't look like that in MY garden!" can't be taken at face value 
if 'that' is a photograph -- whether seen in a catalog, book, or slide show, 
or especially on a website like mine [which could be another thread 
entirely!].  Observations need to be human-eye-on-actual-flower.  The SAME 
human eye, with observations close enough together in time to avoid problems 
of memory distortion.  If you saw something in bloom in your own garden one 
spring, saw a picture of that same cultivar during the year, and then saw the 
flower again in a display garden the next spring -- can you be sure the 
memory you are drawing on hasn't been influenced by the picture? 

To get comparable colors for seedling records, I used the same type of film, 
the same lab, and instead of taking pictures throughout the day as each 
flower reached peak form, I'd shoot a full roll in late morning when the 
day's flowers had opened but not started to fade.  That provided consistent 
lighting conditions for each roll and to compensate for processing variations 
I included a shot of the Macbeth Color Chart. [You should have heard the 
lecture a new employee at the local camera shop got when he took it upon 
himself to save me a few cents per roll by sending my film to a processor 
other than the one I'd specified.  I had the shots of the color chart to 
prove their processing wasn't as accurate and the owner had show 'n' tell 
material to explain the tradeoffs between quality & cost.]


Removing the Photo Factor, we also remove much of the Myth. Now, assuming 
that we're dealing only with first-hand observations, there are factors that 
really do affect the expression of pigments:

pH -- the expression of some anthocyanidins is affected by pH.  Hydrangeas 
are probably the best known example.  There have been reports of this effect 
in iris, to a lesser degree, but although my own observations suggest that it 
is a factor I'm not aware of any definitive studies.  

Sunlight & Temperature #1 -- strong sunlight and low [but above freezing] 
temperatures during bud formation increase the intensity of pigments, 
especially the yellows.  I picked up this tidbit from a friend who had been 
in the greenhouse business and found that it did, indeed, explain phenomena 
occuring in my iris gardens. [One spring, we had a couple of weeks of 
overcast days during bud formation and WHITE CHOCOLATE's normally dark 
chocolate beard was merely a yucky brownish-violet.]

Sunlight & Temperature #2 -- after the flower has opened, strong sunlight and 
high temperatures can hasten fading.   It's very hard to separate these two 
factors, because beds with the strongest light also tend to be warmer -- but 
I've been able to set up controlled experiments where the ONLY difference was 
the amount of shade and those in partial shade held the color much better 
than those in full sun.

Water/Expansion -- arilbreds, expecially, are noted for continuing to expand 
after the flower has opened and thus to undergo dilution of color.  I've 
noticed a similar, although less pronounced, effect in TBs.  If they don't 
get enough water, the last flowers to open are both smaller and more 
intensely colored when they first open.  

 
These are just a few factors to start the discussion, I'm sure others can 
think of more.

Sharon McAllister

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