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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><a
href="http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2007/11/27/HOA2TI0H4.DTL">http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2007/11/27/HOA2TI0H4.DTL</a><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<h1><b><font size=6 face="Times New Roman"><span style='font-size:24.0pt'>Plants
send and receive signals in living color<o:p></o:p></span></font></b></h1>
<p class=byline><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Ron Sullivan,Joe Eaton<o:p></o:p></span></font></p>
<p class=date><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Tuesday,
November 27, 2007<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'><span
id=articlebody>Enjoy that sunset or that Rothko painting? Thank a plant. <o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Speaking
metaphorically, mammals opted out of color vision when we were scurrying around
in the dark, dodging dinosaurs; your dog doesn't see rainbows as well as you do
because our common ancestor didn't. But our closer primate ancestors had an
advantage if they could recognize ripe fruit in a rain forest, and plants advertise
their fruits' mature sweetness and their seeds' readiness for distribution by
suffusing them with color. Color vision had evolved previously in invertebrates
and vertebrates both, and some mammal lineages tapped back into that latent
capacity. <o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>In fact,
as we animals co-evolved with plants, well-advertised fruits gained better seed
distribution via mammals and birds, and poster-bright blooms further
strengthened the partnership by helping pollen get distributed to conceive
those seeds in the first place. <o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Flowers
are a plant's pollination advertising campaign, and every color sends a message
to a particular kind of pollinator. Biologists recognize different
"pollination syndromes," combinations of flower color, shape, scent
and blooming time, fine-tuned to the senses of bees, butterflies, birds or
bats.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Birds
have excellent color vision. Bird-pollinated flowers (<st1:State w:st="on"><st1:place
w:st="on">California</st1:place></st1:State> fuchsias, for example) are often
red, not so much because birds prefer red as because bees don't. Bees aren't
red-blind, but they have more trouble picking out red flowers from green
foliage than they do blue ones, so it's more efficient for them to specialize
in blue flowers.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Bees can
also see into the ultraviolet. Some flowers that look yellow or white to us
appear purple or blue-green to them. Bee flowers often have nectar guides -
petal marks pointing to anthers and pistils, like arrows on a runway - that are
invisible to humans, but clear as day to a bee. Although hummingbirds and some
flower-visiting bats have UV vision, "their" flowers lack such
signals. Bird flowers are also less likely to be scented, since most birds lack
a well-developed sense of smell.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Butterflies
vary; some prefer yellow and blue, others blue to purple. Bats and hawk moths
go for white flowers. Red-flowering scarlet gilias produce paler flowers when
migrant hummingbirds depart and moths replace them as pollinators. North
American columbines, sorting themselves into new species, have evolved new colors
to attract new kinds of pollination partners.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Color
signals can be switched off as well as on. In plants as diverse as trillium,
lantana and Texas bluebonnet, flowers change color once they've been
pollinated, advising prospective customers that the nectar bar is closed.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Sometimes
plants use specialized leaves to attract pollinators. The showy
"flowers" of poinsettia, heliconia and bougainvillea are not flowers
at all but pseudanthia made of bracts - modified leaves.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Leaf
colors have other functions. The default is green, of course, from the
chlorophyll that manufactures a plant's food. Some variations on green are not
a good thing: a chlorotic (yellow) leaf usually signals a deficiency of
nitrogen, magnesium or iron. But healthy plants can have vividly multicolored
leaves: Consider the coleus and the croton.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Those
colors derive from pigments stored in microscopic vacuoles within the cells of
the leaf. Most common are anthocyanins, which range from pink through red and
purple to blue and occur in flowers and fruits as well as leaves. The pigment
overlies a leaf's chlorophyll and doesn't interfere with photosynthesis.
Anthocyanins are believed to screen out harmful levels of UV radiation.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>In a
minority of plants, the active ingredients are betalains, used by botanists as
markers of relationships among diverse-looking forms. Nepenthes, those strange
carnivorous hanging-pitcher plants, got moved all the way to a different order
because their red mottlings are betalains. These pigments, usually purple, red
or orange, are also what beets (including Swiss chard), ice plants, purple
prickly pear cacti and bougainvillea have in common. Their function is obscure,
but they might be antifungals. <o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Some
leaves are two-toned - green above, purple below. This may allow forest-floor
plants to make the best of low-light conditions, bouncing light waves back into
the leaf's photosynthetic cells.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Don't
forget the structural colors. Silvery leaves get their color from hairs called
trichomes, which reflect infrared radiation that might otherwise cook the leaf.
They're often associated with hot or arid locations, as with the Hawaiian
silverswords. Some bluish leaves have a waxy coating that may waterproof the
leaf, filter UV radiation or reflect infrared radiation.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>A new
exhibition at the San Francisco Conservatory of Flowers, "Color: A Winter
Carnivale," showcases the colors of flowers, fruit and foliage. It
features ambient calliope music, carousel animals (from local carver Oscar
Pivaral) and a Wheel of Botanical Fortune. <o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Two years
in the making, "Color" represents a collaboration between Curator of
Education Lisa Van Cleef and designer Anjel Van Slyke. "I ran around to
all the Bay Area nurseries asking, 'What's in bloom?'" says Van Cleef.
"It's not just about the flowers - the foliage contains so much
color."<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Van Cleef
says the exhibition is designed to appeal to kids as well as adults: "How
do we get kids as excited about plants as they are about animals? We need to
show them how to look at the ordinary. When they get out of here, they'll see
plants differently."<o:p></o:p></span></font></p>
<p><i><font size=3 face="Times New Roman"><span style='font-size:12.0pt;
font-style:italic'>Joe Eaton and Ron Sullivan are freelance nature and garden
writers in <st1:City w:st="on"><st1:place w:st="on">Berkeley</st1:place></st1:City>.
E-mail them at <a href="mailto:home@sfchronicle.com">home@sfchronicle.com</a>.</span></font></i>
<o:p></o:p></p>
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<p id=url><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>http://sfgate.com/cgi-bin/article.cgi?f=/c/a/2007/11/27/HOA2TI0H4.DTL<o:p></o:p></span></font></p>
<p id=pageno><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>This
article appeared on page <strong><b><font face="Times New Roman">G - 8</font></b></strong>
of the San Francisco Chronicle<o:p></o:p></span></font></p>
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