Ask A Scientist© Biology Archive

name         GEORGE
status       other
age          30s

Question -   WHY DO LEAVES CHANGE COLOUR IN THE AUTUMN?(FALL),AND WHAT
DO THE COLOURS COMPRISE OF IF NOT CHLORPHYL?
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Dear George,

http://willow.ncfes.umn.edu/leaves/leaves.htm
http://www.esf.edu/pubprog/brochure/leaves/leaves.htm
http://photoscience.la.asu.edu/photosyn/education/colorchange.html

Sincerely,

Anthony R. Brach

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Anthony R. Brach, Ph.D., brach@oeb.harvard.edu
http://www.herbaria.harvard.edu/~brach/
Flora of China http://flora.harvard.edu/china/
Harvard University Herbaria, 22 Divinity Avenue, Cambridge, MA 02138-2094 USA

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George,

What you see when leaves change color is the appearance of pigments which
are otherwise normally hidden by the presence of green chlorophyll.  The
xanthopylls and cyan colors are pigments that are always present, but as
chlorophyll is broken down/resorbed by a plant, the hidden pigments become
prominent.

Thanks for using NEWTON!

Richard R. Rupnik
Internal Quality Auditor
Lucent Technologies
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In the fall with the diminishing daylight and cooler temperatures, deciduous
trees begin to shut down chlorophyll production.  There are other colors in
the leaf besides the green of chlorophyll, such as carotenes (yellow/orange),
xanthophylls (yellow) and anthocyanins (reds).  When the chlorophyll goes
away, the other colors that were there all along can show through.
Eventually, the leaf is sealed off from the tree and it turns brown and falls
off.  In the spring, when the days get longer and the days warmer again, the
tree begins to produce chlorophyll again.
Van Hoeck
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A brief outline is at
http://www.flash.net/~johnrtnc/fall.htm

J. Elliott
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