Nature Bulletin No. 603-A   May 8, 1976
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation

****:POLLEN AND POLLINATION

Almost everybody loves a flower. Commonly the word "flower" 
suggests showy colors, symmetrical designs, fantastic shapes, fragrance 
and nectar. However, these pleasing features are mainly lures to attract 
insects upon which plants depend to carry their pollen from one flower 
to another. This is pollination, a function essential to the life line of the 
plant and the production of seeds and fruit which we use as food. Many 
other plants, such as grasses and our common trees, have wind-borne 
pollen. Even though their flowers are inconspicuous, colorless and 
odorless, they have pollen -- and that makes them flowers.

Pollen is the yellow stain on a youngster's nose after he sniffs a 
dandelion. It is the shower of golden dust from blooming ragweeds in 
late summer which causes most of our hay fever cases. From 
midsummer through the first heavy frost, air samples are taken and 
daily pollen counts are published. Pollen can be blown by west winds 
from Illinois across Lake Michigan or carried hundreds of miles out to 
sea. In general, wind-borne pollen is abundant, light and dry; while 
insect-borne pollen is sticky, heavy, and produced in small quantities.

A pollen grain is the male sex cell of a flowering plant. On the mature 
stigma of a flower of the same species it germinates and a pollen tube 
grows down through the style to unite with an ovule, or egg cell, which 
then develops into a seed. For example, a single strand of the 
thread-like silk of an ear of corn, sometimes over a foot long, is a 
greatly elongated style. A pollen tube pushes its way down this entire 
length in a matter of a few days to fertilize one kernel of corn. In 
contrast, some oaks require almost a year for their pollen tubes to grow 
one-eighth of an inch.

The great majority of the world's flowers are cross-pollinated. They can 
be divided up according to the way pollen is carried from one plant to 
another. We have bee flowers, moth flowers, fly flowers, beetle flowers 
and hummingbird flowers. In some of our water plants, such as eel 
grass, pollen is floated from one flower to another. In the tropics there 
are even bat flowers.

Bee flowers are usually blue or yellow -- colors which are brightest to a 
bee's eye. Some of them provide a special lip or landing field with 
guide lines leading to the nectar stores deep inside. As the bee sips the 
nectar, the body hairs pick up pollen and transfer it to the next flower 
visited. Butterflies are often attracted by red or orange flowers -- colors 
which bees cannot see. Moths, unlike bees and butterflies, hover over 
flowers at dusk and night, preferring those that run to shades of white 
and very heavy fragrance. Some hawk moths have tongues several 
inches long. Fly flowers are mostly dull-colored and have rank odors. 
Some smell like spoiled meat, fish oil or stale tobacco.

The pollen grains from various plants differ greatly in size, shape and 
surface markings. Some, like those of the pines, have air bladders which 
make them unusually light and buoyant. Grass pollen is smooth with a 
single pore, sunflower pollen is spiny, and pigweed pollen, when 
magnified, looks like the markings on a golf ball.

Pollen grains are protected by thin, glassy, plastic covers which are 
highly resistant to decay. Actually, these tiny, fragile-looking granules 
are more durable than any other part of a tree. As the wind blows them 
about and they settle in peat bogs or the beds of ancient lakes, a record 
is preserved of the kinds of plants that grew here in the past. By 
identifying and counting these pollen grains, we can read the changes 
which have taken place over vast periods of time.

Which came first, the bee or the flower?