Page 134 - Photosynthesis: The Green Miracle

denly become aware of color change. As leaves change their colors and
fall from the trees, we find ourselves faced by the brightest of pictures.
Bright green trees turn yellow, red, and brown within a few short days.
But what causes this color change, and why do leaves fall from the trees?
All leaves, be they yellow, red, purple or green, are colored by the
various pigments they contain. The best-known among plant pigments is
without doubt chlorophyll, which gives leaves their characteristic green

color and also plays a very important role in photosynthesis, as you have
seen throughout this book. In moderate climates, leaves begin to change
color with the coming of autumn. The yellows, oranges, reds and finally
browns that replace the green in leaves are the product of the yellow and
orange pigment carotene. A pigment called anthocyanin also plays a part.
Together, these three pigments give leaves and summer flowers their col-
ors.
The green of chlorophyll in leaves is so strong that it masks the exist-
ing yellows and oranges of the leaves. Before plants shed their leaves in

the fall, they re-absorb the useful substances contained in them. One of
the consequences of this is that chlorophyll begins to break down. Since
chlorophyll no longer predominates at this stage, the yellow and orange
pigments, which had not been apparent before, now begin to be seen.
When leaves come to the end of their life spans, the pigment antho-
cyanin starts to increase, turning some leaves from their normal green to
a light reddish-purple. Anthocyanin pigments vary from red to purple,

and the red, blue and purple regions of a plant are entirely their responsi-

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