|| by Greg
Arrowhead High School
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Why study pollen? Fossil pollen grains are identifiable more than 100 million years after they were formed. Scientists study these grains to help determine the climate and ecology of past geological eras. Ancient hieroglyphics record the application of pollen in the rituals of ancient civilizations. Since the mid-19th century, air-borne pollen was recognized as detrimental to health for some humans. People still blame certain plants—and their pollen—for seasonal hay fever and allergies. Pollen produces the fruits, grains, and vegetables that keep us alive and healthy. Pollen is an important part of the human and non-human environment. Palynology is the study of pollen and spores; it examines their structure and formation, means of dispersal, and preservation under certain environmental conditions.
|Pollen is not plant sperm. It is a container which houses the male gametophyte generation of an angiosperm or gymnosperm (figure 1). This module will focus on the pollen from angiosperms. Pollen is formed within the anthers of a flower through the process of meiosis. As such, it contains one-half the genetic material of the parent plant. In order to form a complete, new plant, it must combine its genetic material (the DNA) with the DNA of an egg of the same species.|
|This combination of genetic material is called fertilization. For fertilization to occur, the pollen must get from the anther to the stigma. Once on the stigma, the pollen grain sends a pollen tube down the style and to the ovary where the pollen’s genetic material combines with the egg’s genetic material (figure 2).|
This will develop into a seed which will grow into a new plant. The problem in all of this is in getting the pollen from the anther to the stigma of the same species; most pollen grains never make it. A plant’s pollen can make this important journey in one of two ways: by the wind or by animals. Wind-dispersed pollen is generally smaller than animal-dispersed pollen. Pollen is carried by mammals (including humans), birds, and at least 16 orders of insects. Among insects, the honey bee is one of the best known and most important pollinators. Some bee species carry a pollen load of 100 to 200 mg—approximately one-half their body weight!!! The hairs of one bee can carry between 250, 000 and 6, 000, 000 grains, depending on the pollen source. The size of pollen varies from a diameter of 5 micrometers in forget-me-nots to over 200 micrometers in members of the cucurbits. The size is also variable within a species and even within a single flower. The small size of pollen translates into ease of transport for the genetic material. However, the unreliability of any particular grain reaching a target means that they must be produced in very large numbers…especially with wind pollination and less so with insect pollination. This small size can make identification difficult. Using light microscopy, the identification of pollen grains is sometimes limited to a family or generic level, but there are occasions when identification to species is possible.
To retrieve Student Lab Sheet, click HERE!
To retrieve Pollen Record Sheet, click HERE!
Stanley, R.G. and Linskens, H.F. 1974. Pollen: biology, biochemistry, management. Springer-Verlag, New York. 307 pp.
Moore, P.D., Webb, J.A., and Collinson, M.E. 1991. Pollen Analysis, 2nd ed. Blackwell Scientific Publications, Boston. 216 pp.
Cronkite, D. Personal Communication. WWI Academic Director; Hope College, Holland, Michigan.