How to Identify Pollen Grains

Pollen grains have varying structures and ornamentation that aid in identification.

Pollen grains are male reproductive cells from plants, the botanical equivalent of the mammalian sperm. The genetic material is encased in a tough protective casing made of sporopollenin, which resists desiccation and the effects of acids, bases, and other environmental factors. Pollen is produced in the stamens of flowers and transferred by insects or wind. Windborne pollens are the primary agents of hay fever, since people become allergic to the specific proteins different pollens contain. Pollen grains have varying shapes and morphologies, such as apertures and sculptural and ornamental features, which are helpful in identification.

Things You'll Need

• Pollen grains
• Microscope slide
• Silicone grease or glycerin
• Cover glass
• Eyedroppers
• Forceps
• Ethyl alcohol
• Distilled water
• Safranin O or Calberla's solution
• Fast-drying nail polish
• Light microscope
• Pencil
• Eraser
• Paper
• Book on pollen grain identification

Instructions

Collect and Prepare Pollen Sample

1. Clean a microscope slide with ethyl alcohol. Coat about one square inch in the center of the microscope slide with silicone grease or glycerin. Put the slide outdoors for 24 hours where it will be undisturbed but exposed to the open air to collect pollen grains. You could also collect pollen from flower stamens with a small paintbrush.

2. Bring the slide indoors and use the eyedropper to put a drop of Safranin O or Calberla's solution on the coated area of the slide. Use the forceps to lower a cover glass over the drop of stain. Another method would be to touch the paintbrush to a few drops of distilled water placed on a slide and mix to release the pollen grains into the water. Use an eyedropper to transfer some of the pollen-containing fluid to the middle of another slide and add a drop of stain, then lower the cover slip in place.

3. Paint quick-drying nail polish in a narrow strip around the edges of the cover slip to prevent the sample from drying out.

Identify

1. Place the prepared slide on the stage of a compound light microscope. Examine the area under the cover slip under low magnification to find pink-stained pollen grains.

2. Switch objectives to higher magnification, finding and focusing in on individual pollen grains. Scan the field to see how many different sizes, shapes and morphological differences are present. For examining individual pollen grains, it may be necessary to use the oil-immersion lens.

3. Draw pictures of the different pollen types, including pores, furrows, ridges and various kinds of ornamentations on the exsine, the outer wall of the pollen grain. These may include depressions, small pits, granules, bud-like structures, club-shaped structures, spines, and network-like features.

4. Compare drawings and the observed pollen grains with drawings and photographs in pollen atlases or reference books. It is often impossible for a novice to identify a pollen grain any further than the plant family it belongs to. It takes an expert with access to a reference collection of positively identified pollen grains to identify pollen grains to genus or species level. Write the identifications next to the drawings of the pollen grains. Label the slides and keep for reference if desired.

References

• "Amazon Pollen Manual and Atlas"; Paul A. Colinvaux, et al.; 1999
• Access Excellence Summit: Pollen Collection and Identification
• U.S. Department of Agriculture: Research Techniques
• "Hayfever Plants"; Roger P. Wodehouse; 2007
• "Forensic Science: Fundamentals and Investigations"; Anthony J. Bertino, Patricia Nolan Bertino; 2008

Resources

• Read this Article in Spanish