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<DIV id=printReady><SPAN class=storyheadline>JUDY JESSOP: Pollen May Be
Annoying, But It Is Extremely Important</SPAN><BR><BR><!--SIGINSERT--><!--PIXINSERT-->Lightweight floating
pollen that puffs with each step, speckling the air we breathe, causes havoc
with those of us that have allergies.
<P>It is, however, the only way that many trees and plants achieve pollination.
Wind pollinators must dump huge amounts of pollen into the air.
<P>This strategy is necessary to raise the possibility of some grains finding
the right flowers, so germination can take place. Ragweed is at the top of the
list of allergy, producing wind pollens. Others such as oak, birch, maples and
grasses may also trigger allergies. Now that summer has arrived, though, and
many wind-pollinators are finished, allergy symptoms are settling down.
<P>Not all pollen triggers hay fever. In general, those of us with such
allergies can be friends with all the plants that depend on insects, birds and
other animals to pollinate their flowers. Such plants have heavy, sticky pollen
that clings to any volunteers drawn to sip sweet nectar. The major ways that
pollen is transported in our region of the state is by insects, birds and the
wind.
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<DIV id=printReady1>Flowers that depend on insects use many different strategies
to attract them. Some flowers generalize -- any insect will do, so their
structure may be quite simple, with no specialized features.
<P>The tulip is a good example. It has a large wide cup of petals with long
anthers holding the pollen. Any insect crawling over the anthers, as it looks
for a sweet reward, will pick up a bit of sticky pollen to transport onward.
<P>Some flowers specialize to attract specific insects, such as bees. These
flowers often have a lobe that acts as a landing pad and deep-throated petals.
The pollen-laden anthers are located at the top of the flower throat, dusting
the backs of the bees as they enter. Bees are most sensitive to the violet end
of the color spectrum, so many bee-pollinated flowers have blue or violet
markings.
<P>Another strategy, used by some flowers, is to display showy brackets, or
modified leaves, that attract attention (such as the dogwood). These bright
white flags also provide landing platforms for insects as they sip nectar while
pollinating the tiny flowers nestled in the center.
<P>Flowers can develop some interesting relationships with their pollinators.
The plants of the yucca family, for instance, depend on a single species of moth
for successful pollination.
<P>The female yucca moth gathers a ball of pollen and stuffs it into the
cup-shaped stigma of each flower. She then lays a few of her eggs in the pollen.
When the moth eggs hatch, the larva consume a small number of the developing
seeds, but this loss is outweighed by the benefit of having such an effective
pollinator.
<P>Another interesting aspect of this symbiotic relationship is that if the moth
lays too many of her eggs on the stigma, the flower will abort and drop off to
the ground -- the plant's way of selecting against moths that over-lay to the
detriment of the yucca's regeneration.
<P><STRONG>Bird Pollination</STRONG>
<P>Many flowers depend on hummingbirds for pollination. These flowers are often
deep throated, and the hummingbird hovers while reaching deep inside for nectar.
<P>Bird-pollinated flowers have no landing platform, since hummers need not land
to feed. Anthers are often dangled to dust the bird's head as he or she feeds on
the nectar. These flowers are often red, orange or deep pink, colors that
attract the birds but are inconspicuous to most insects.
<P>The nectar of hummingbird flowers is relatively weak, about 25 percent sugars
with high levels of sucrose. Insect-pollinated flowers normally produce highly
concentrated nectars dominated by fructose and glucose.
<P><STRONG>Wind Pollination</STRONG>
<P>As I mentioned earlier, many of the trees and plants that pollinate in early
spring depend on the wind to spread their pollen. These trees and plants may be
either gymnosperms (nonflowering) or angiosperms (flower-producing).
<P>Pine trees are an excellent example of gymnosperms. These trees do not have
flowers. Instead, they reproduce by developing cones, which are modified leaves.
Some of these cones are male, producing pollen, while others are female, with
each scale of the cone housing two eggs.
<P>The male cones are present only in early spring and now litter the ground.
Pine trees are particularly conspicuous when pollinating because the pollen is
yellow, and here in the Sandhills, we have lots and lots of pine trees -- the
reason that at times even the air swirls in yellow puffs.
<P>Interestingly, pine pollen is not allergy-producing to most people. It just
gets blamed because there is so much and it is so yellow.
<P>Other wind pollinators, the angiosperms, produce flowers, but the flowers are
not scented, and they don't produce nectar. The flowers are also very simple and
often do not even have petals. The red maple is an example. Often these plants
bloom before the leaves emerge to allow wind-borne pollen easy access to the
flowers.
<P><STRONG>The Precious Cargo</STRONG>
<P>Pollen is amazing stuff, each grain a complicated little travel capsule. Its
important occupants are two male sperm cells.
<P>The outside wall (called the exine) is very tough material composed of waxes
and proteins. It protects its precious cargo from solar radiation and
dehydration, as the cell bumps around in search of the right flower for
pollination. Exines have either pores or special ridges where the case is
thinner -- an important feature when the pollen finds the right mate.
<P>Packed inside the exine is an inner layer of cellulose (the intine) much like
a cell wall. Inside this layer are a few cells. One of these cells is very
specialized. It is a reproductive cell with two nuclei. One nucleus will produce
a pollen tube, and one will divide into two sperm cells.
<P>In angiosperms, every grain of pollen that successfully reaches the flower of
its own species still has work to do. When it arrives on the stigma (the part of
a flower that receives pollen), the tube cell in this grain of pollen begins to
elongate, exiting the outer wall of the pollen grain through a pore or ridge.
<P>The tube continues growing down into the center of the flower toward the
unfertilized eggs. This single-celled tube can be quite long in some plants. In
corn, for example, the tube must grow as much as 12 inches to reach the eggs.
<P>As the tube grows, the two sperm cells travel down the tube toward the tip.
When the tip of the tube reaches an ovule (female reproductive cell), it bursts,
releasing the two sperm cells.
<P>One of these sperm cells will unite with the egg, making a fertile seed. The
other will unite with another cell, which produces food that is stored around
the seed. The food store is high in starch, protein and oils. Such grasses as
corn are so high in stored food that they have become a main staple of the human
diet.
<P>In gymnosperms (such as our pines), during the period of time that pollen is
being released to the wind, the scales of female cones open temporarily to
receive pollen, and the pollen grain is drawn directly into the egg. The female
cones then close during fertilization and maturation.
<P>There are many intricate, amazing and important things that are going on
during pollination -- each single microscopic pollen grain a complex structure.
Yet one pinch of pollen powder holds thousands of grains. It may at times wreak
havoc with those of us with allergies, but without it where would we be?
<P><EM>Contact Judy Jessop by e-mail at jgjessop@gmail.com.</EM></P></DIV></DIV>
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<DIV><FONT lang=0 face="Gill Sans MT" size=2 FAMILY="SANSSERIF"
PTSIZE="10"><BR><BR><BR><BR><BR>Laurie Davies Adams<BR>Executive
Director<BR><B>Pollinator Partnership </B><BR>423 Washington Street, 5th
floor<BR>San Francisco, CA
94111<BR>415-362-1137<BR>LDA@pollinator.org</FONT><FONT lang=0 face=Arial
color=#000000 size=2 FAMILY="SANSSERIF" PTSIZE="10"><BR><BR></FONT><FONT lang=0
face="Gill Sans MT" color=#0000ff size=4 FAMILY="SANSSERIF" PTSIZE="14"><B><A
href="http://www.pollinator.org/">www.pollinator.org</A></B></FONT><FONT lang=0
face="Gill Sans MT" color=#000000 size=2 FAMILY="SANSSERIF"
PTSIZE="10"></B><BR><A
href="http://www.nappc.org/">www.nappc.org</A><BR><BR></FONT><FONT lang=0
face="Gill Sans MT" color=#000000 size=3 FAMILY="SANSSERIF"
PTSIZE="12"><B><I>National Pollinator Week is June 22-28, 2009. <BR>Beecome
involved at <A
href="http://www.pollinator.org/">www.pollinator.org</A></I></FONT></B></DIV></FONT><DIV CLASS="aol_ad_footer" ID="6e4b1407f9611b631c4949fc92a22462"><br/><font style="color:black;font:normal 10pt arial,san-serif;"> <hr style="margin-top:10px"/><B>A Good Credit Score is 700 or Above. <A HREF=http://pr.atwola.com/promoclk/100126575x1221823322x1201398723/aol?redir=http://www.freecreditreport.com/pm/default.aspx?sc=668072&hmpgID=115&bcd=JulystepsfooterNO115>See yours in just 2 easy steps!</A></B></font></DIV></BODY></HTML>