[Pollinator] Pollen May Be Annoying, But It Is Extremely Important

[Ladadams at aol.com]

from ThePilot.com
 
 
JUDY JESSOP: Pollen May Be  Annoying, But It Is Extremely Important

Lightweight floating  pollen that puffs with each step, speckling the air 
we breathe, causes havoc  with those of us that have allergies.  
It is, however, the only way that many trees and plants achieve 
pollination.  Wind pollinators must dump huge amounts of pollen into the air.  
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.  
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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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.  
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.  
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.  
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.  
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.  
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.  
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.  
Bird Pollination  
Many flowers depend on hummingbirds for pollination. These flowers are 
often  deep throated, and the hummingbird hovers while reaching deep inside for 
nectar.   
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.  
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.  
Wind Pollination  
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). 
 
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.  
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.  
Interestingly, pine pollen is not allergy-producing to most people. It just 
 gets blamed because there is so much and it is so yellow.  
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.  
The Precious Cargo  
Pollen is amazing stuff, each grain a complicated little travel capsule. 
Its  important occupants are two male sperm cells.  
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.  
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.  
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.  
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.  
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.  
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.  
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.  
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?  
Contact Judy Jessop by e-mail at jgjessop at gmail.com.

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 





Laurie Davies Adams
Executive  Director
Pollinator Partnership 
423 Washington Street, 5th  floor
San Francisco, CA  94111
415-362-1137
LDA at pollinator.org

_www.pollinator.org_ (http://www.pollinator.org/) 

_www.nappc.org_ (http://www.nappc.org/) 

National Pollinator Week is June 22-28, 2009. 
Beecome  involved at _www.pollinator.org_ (http://www.pollinator.org/) 
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