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Re: Beard Hair structure and effects on colour

  • Subject: [iris-photos] Re: Beard Hair structure and effects on colour
  • From: "irischap" irischapman@netscape.net
  • Date: Mon, 24 Jan 2005 03:14:32 -0000

Neil, do you have references for this I can check out?

The beard hairs as a monofiliment is what I have been thinking but I
would like to have some science reference to refer to. Certainly the 
beard hairs are more transparent then the cell walls of the
epidermis.This structural/transparency would certainly enhance any
pigments inside them. I would think that the same apearance of colour
in epidermal layer would require the same structure. I can't see  that
happening. Just adding more pigment to the cells of the epidermis
would be one step in getting redder iris but we would be missing the
difference in cell structure and the transparency brought about by the
thinner tissue. In addition the beard hairs affect colour perception
by bouncing light from one filimant to another so there is a reduction
of escaping light reflected back to the eye.This would have the effect
of increasing perceived intensity of pigments. 

Chuck Chapman


--- In iris-photos@yahoogroups.com, "Neil A Mogensen" <neilm@c...> wrote:
> Robin, this may show up in the sort by "Thread" far from your entry,
but I did want to respond to your question about the beard, "white to
cream tipped flame" or something close to that phrasing in the
description of F o F. 
> The beard hairs are an extension of epidermal, top layer, cells of
the fall, I think--although I am not totally positive of that.  In
aril species it certainly is so, as the beard hair is of the epidermal
cell, stretched upward, monofiliment--only one cell, which is part of
the epidermis.
> In Eupogons--bearded irises that fall in the classes other than
aril--the beard hairs are shaped like a baseball bat, standing on the
handle end.  They are composed of many cells, probably all epidermal
in origin.
> All the cells of the iris, all the way from the remotest root tip to
the tip of the standards, have the same genetic makeup.  
> What gets expressed, however, in any one cell depends on which genes
are switched on, which are switched off.  An obvious example of this
is that in normal development, you aren't going to see standards
growing out of roots, or leaves emerging where the style arms are
supposed to be.
> We have pretty much ignored the whole question of switching
mechanisms and control in our discussions of color, but in any iris,
any color variation from part to part has to do precisely with those
mechanisms.  Switching on, switching off "genes"--control genes--are
what make plicata and luminata patterns possible, for example.
> In beards, there must be similar mechanisms that make beard hairs
different colors front to back of the beard, bottom to top of the
beard hair.  In a hair or beard filament if the base is white, the
middle is yellow, the tip is "flame," which may or may not be Lycopene
present, what may be going on is that synthesis of carotenoids is
suppressed entirely somewhere in a colorless part of the synthesis
pathway.  In the yellow part I would assume, based on what Chuck
Chapman has suggested, the synthesis proceeds to either a xanthophyll
or beta-Carotene pigment, with the tip either containing some
Lycopene, or more likely a heavy concentration of various yellow to
richer than yellow Carotenes and/or Xanthophylls.  If tangerine
(Lycopene) "tttt" is present, I would expect to see something more
definite than what is in the "flame" description.  Many non "tttt"
varieties have a hot color in the deepest part of the throat in the
beard tips.  
> I'd love to see a pigment analysis of those beard tips.  The result
could be quite interesting.
> Neil Mogensen  z 7 western NC mountains

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