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POLLEN

POLLEN. Though palynology, which denotes the study of pollen and spores, is not a household word in Texas, the allergic effects of airborne pollen and spores are well known throughout the state. In technical terms, pollen is the microscopic mature or immature multinucleate gametophyte generation of seed plants. Its most important function is to carry the sperms needed for plant reproduction. A spore, on the other hand, is a cellular agent of asexual reproduction. Spores and pollen are similar in shape and size, in their ability to remain preserved in sediments for millions of years, and in their ability to be produced and dispersed by the millions. In addition, each spore or pollen grain type is morphologically unique to its plant species.

Each year thousands of Texans are immobilized by the crippling effects and allergic reactions caused by inhaling pollen and spores. It is estimated that the pollen count exceeds 500 pollen grains and spores per cubic meter of air during an average spring day in Texas. On those days, a non-active individual who spends much of the time indoors will inhale about 7,200 pollen grains during a twenty-four-hour period. If that same person were active or working out-of-doors, the amount of inhaled pollen would be many times higher than that amount. The reason we inhale so many pollen grains and spores is that a single blooming tree, such as a pine or oak, produces and disperses between five and ten billion airborne pollen grains within a few days. Although trees produce much pollen and are often popularly considered the primary sources of airborne allergens, however, fungi produce more. In the moist regions of Texas hundreds of types of fungi grow, mature, and disperse their spores into the air each day. The bracket fungus (Ganoderma applanatum), for instance, discharges 30 billion spores a day. Its normal growing season begins in early May and continues until the end of September. This means that just one plant of this fungus can discharge a total of 4.5 trillion spores in one season (a figure equivalent to one spore per dollar of the national debt). In the springtime thousands of weeds, bushes, and trees cast billions of pollen grains to the wind. Some of the main offenders include ash, elm, pine, oak, pecan, hickory, poplar, and walnut trees. Each of these plants produces millions of airborne pollen grains that are cast adrift in wind currents. A few months later, other species of pollen-producing weeds and shrubs mature. These include the grasses, composites, sedges, cattails, goosefoot, and other plants. In late summer and early fall, ragweeds and other species of grasses fill the Texas air with new types of pollen. During the autumn and winter there is relief for some sufferers, but for others, such as those living along the Balcones Escarpment and in the Hill Country west of Austin, the winter pollen cycle is the worst. Junipers begin to bloom by October and continue producing airborne pollen late into the winter. Worst of all, throughout most of the year millions of fungal spores are produced and dispersed by some species of mold and mildew.

Texans suffer from the effects of pollen and spores because these microscopic cells are rich in different types of proteins. Once inhaled, pollen and spores rupture when they come in contact with moist nose and lung membranes. The body's defense system goes on full alert and treats the newly released proteins as foreign substances. Part of the human immune system consists of mast cells, which line the walls of the respiratory system and release histamines and other compounds into the bloodstream as a defense. This immune response causes runny noses, congestion, itching, and sneezing.

The same pollens and spores that give some people runny noses, however, provide valuable data for palynologists. Information about them is helping Texas geologists locate new oil and gas deposits, helping climatologists understand cycles of weather and environmental changes during the last 30,000 to 50,000 years, helping archeologists to unlock the secrets of Indian diets and ancient cultural patterns covering the last 10,000 years, helping Texas farmers and honey exporters to determine the quality and floral sources of honey produced in Texas, and helping United States Department of Agriculture scientists working in Texas to find new ways of eradicating a variety of agricultural insect pests. Economically, the most important application of palynology in Texas is in the oil and gas industry. During the first thirty years of the twentieth century, petroleum exploration in Texas concentrated mostly on the recovery of oil and gas reserves from shallow deposits. Drilling was based on a knowledge that oil and gas flow upward through sediments until they reach an impervious layer, and that potential petroleum sources often could be identified by surface features or exposed stratigraphy revealing subsurface faults, salt domes, and anticlines. During the early years of the Texas oil industry, stratigraphic locations of oil and gas-bearing zones from one region to the next were based mostly on similarities in the composition of strata. These approaches worked well for shallow deposits, but as petroleum companies began drilling deeper wells and exploring new regions of Texas, they discovered that previously used methods no longer worked. Out of frustration a Shell Oil geologist named Thomas Grimsdale searched for a new technique and discovered that fossil pollen was an excellent stratigraphic indicator. Since that time, fossil pollen has become a primary tool used for stratigraphically correlating oil and gas deposits throughout Texas. Today the state is an important world center for oil and gas research, and employs more professional palynologists than any other region in the world.

Texas archeology has also benefitted from pollen data. Dirt and debris caught in rocks used during prehistoric times to grind seeds into flour are now routinely examined for pollen. From such studies we have learned that ancient Texans collected and used the seeds of a wide variety of wild and domesticated plants to make flour. Pollen is a useful key to the types of seeds ground into flour because during the collection of many seeds such as corn, pigweed, amaranth, and sunflower, pollen is collected and mixed with the seeds. At archeological sites in West Texas, archeologists have found flint scrapers and knives that still carry dried plant sap cemented to their edges. Microscopic examination of the dried sap has revealed the presence of organic plant debris, including pollen. From this type of study we have been able to speculate which flint tools were used by ancient Texas Indians to cut plants such as cactus, yucca, and agave plants. Arid regions in Texas have also yielded our best records of prehistoric human diets. For the most part, these dietary records have come from coprolites (preserved feces) found in the ancient latrine areas of prehistoric sites in and around the Amistad Reservoir region near Del Rio. Coprolites containing large amounts of pollen from insect-pollinated plants indicate that prehistoric Indians collected and ate flowers as part of their food. Palynologists can make these assessments because modern tests show that eating flowers or large quantities of honey, can introduce large quantities of pollen into the human digestive system. However, because honey seems an unlikely food source in prehistoric Texas since the European honey bee was not introduced into the Americas until after 1620, we believe the pollen in coprolites came mostly from eating flowers. Fossil pollen studies are helping archeologists in other ways. Fossil pollen in deposits in Bonfire Shelter, located near Langtry, reveal that the vegetation of that region has changed during the last 12,000 years. We now know from the pollen data that the region west of Del Rio was supported a maximum coverage of grass only twice. During each of those times, grazing conditions were ideally suited for large buffalo herds, and during both periods Indians drove herds of the animals over cliffs above Bonfire Shelter. We believe that these bison were killed by skilled hunters who probably followed the animals south from North Texas and discovered that Bonfire Shelter was an ideal location for stampeding them over cliffs.

In other regions of the state, palynologists are using pollen to study honey. Bees use nectar and pollen as food and to make honey. Because bees rely on local plants to make honey, the pollen in honey becomes a "fingerprint" of the region where the hive is located. Commercial companies that sell honey to the public often test pollen to ensure that their "clover" honey really does come from clover plants and that other types, such as "cactus blossom" and "mesquite" honey, are really made mainly from the flowers of those plants. Pollen is also the focus of a plan designed to reduce the damage to Texas crops by the corn earworm (Helicovera zea [Boddie]), the cabbage looper (Trichophusiu ni [Hubner]), and the boll weevil (Anthonomus grandis grandis [Boehemon]). Each spring millions of adult corn earworm moths hatch in regions of northern Mexico and along the lower Rio Grande valley. The adult moths feed on nectar and pollen before flying to Central and North Texas, where they mate and lay eggs. Studies of the pollen adhering to the bodies of these moths and others such as the cabbage looper tell us the flower types these insects prefer. Once these are known, chemical attractants that mimic the odors of these insects' favorite flowers can be used to capture or kill them before they mate and lay eggs. Studies of the boll weevil reveal that during the winter months the adults survive on a diet of available pollen and other plant foods. In spring they mate and lay eggs on the immature bolls of cotton. Because insecticides are expensive and ecologically unsafe, an alternative now being considered is to capture or kill adult boll weevils during the winter months by using traps baited with their favorite pollen types.

The most recent application of pollen technology in Texas has been in the field of forensics. Currently, Texas leads the nation in the study and use of pollen and spores as forensic clues in criminal and civil cases. One recent application was the recovery of pollen from clothing worn by a murder victim in West Texas. Authorities found an unidentified victim who had been killed elsewhere and then dumped along an interstate highway. There were no apparent clues to identify who the victim was or where he had lived. However, pollen trapped in his clothing revealed that he probably had lived in the central United States or in the Panhandle north of Lubbock. In another recent case, Central Texas authorities seized a supply of marijuana and wanted to know if it had been grown locally or was imported. Pollen studies indicated that the pot could have been grown in a region extending westward from Central Texas to Phoenix, Arizona, and therefore confirmed that the seized drugs were not shipped from a foreign country. See also PREHISTORY, TREES, GRASSLANDS, BEE INDUSTRY.

BIBLIOGRAPHY: 

V. Bryant et al., "Forensic Palynology in the United States of America," Palynology 14 (1990). Vaughn M. Bryant, Jr., and Richard G. Holloway, Pollen Records of Late-Quaternary North American Sediments (Dallas: American Association of Stratigraphic Palynologists Foundation, 1985). V. Bryant and R. Holloway, "The Role of Palynology in Archaeology," Advances in Archaeological Method and Theory 6 (1983). C. Hopping, "Palynology and the Oil Industry," Review of Paleobotany and Palynology 2 (1967). G. Jones and V. Bryant, "Melissopalynology in the United States: A Review and Critique," Palynology 16 (1992). P. Lingren et al., "Adult Feeding Host Range and Migratory Activities of Corn Earworm, Cabbage Looper and Celery Looper (Lepidoptera: Noctuidae) Moths as Evidenced by Attached Pollen," Journal of Economic Entomology 86 (1993). H. Shafer and R. Holloway, "Organic Residue Analysis in Determining Stone Tool Function," in Lithic Use-Wear Analysis (New York: Academic Press, 1979). K. Sobolik, Prehistoric Diet and Subsistence of the Lower Pecos, as Reflected in Coprolites from Baker Cave, Val Verde County, Texas, Texas Archaeological Research Laboratory Studies in Archaeology 7 (1991).

Vaughn M. Bryant, Jr.

Citation

The following, adapted from the Chicago Manual of Style, 15th edition, is the preferred citation for this article.

Vaughn M. Bryant, Jr., "POLLEN," Handbook of Texas Online (http://www.tshaonline.org/handbook/online/articles/sop01), accessed July 28, 2014. Uploaded on June 15, 2010. Published by the Texas State Historical Association.