Pollen
In addition to honey, pollen forms the basis of the honeybee diet. Pollen provides the protein, vitamins and trace elements needed by the colony and its collection can be a good indication of brood rearing. By identifying pollen in one's own honey it is possible to know which plants were foraged at that time (this is known as melissopalynology, an excellent reference from the Apidologie journal details how this is performed).
Pollen carries the male gametes necessary for plant fertilisation from the male anthers to the female stigma. Pollen is usually transferred between plants by the wind or through insects; individual plant species will have adapted to promote either transfer mechanism. The identification of pollen can be determined by both surface structures present and the size and shape of individual pollen grains. The pollen surface (exine layer) may also contain characteristic projections or sculptures. A reference database of pollen slides from local plants is currently being compiled at MUBKA. A method is detailed below showing how the slide is created.
Preparing Pollen Slides (Download this guide for free in PDF format)
If possible use only freshly opened flowers so that contamination from other pollens is avoided. The example below was made using Hawthorne pollen collected in May 2009.
1. Remove anthers from the stamen and place into a small dish. Add a few drops of isopropyl alcohol (IPA) to remove the waxy surface from the pollen grains and to separate them from the anthers. Leave for 10 mins.
2. Melt the glycerine jelly (around 40oC), preferably in a water bath.
3. Mix the anther and IPA solution and take 2 drops of the liquid. Place in one half of the slide and repeat on the other half. One area will be used with stained glycerine jelly mountant whilst the other is unstained.
4. Allow the IPA to dry (1-2 mins on a hotplate) and then rinse the slide with a few drops of IPA to remove plant debris.
5. Allow the slide to dry again on the hotplate. Keep the glycerine jelly and coverslips warm.
6. Place a drop of molten glycerine jelly on a warm coverslip. Slowly lower the upturned slide so that the pollen grains contact the jelly. By keeping the slide at a slight tilt and lowering slowly, the inclusion of air bubbles should be minimal.
7. Leave the slide on the hotplate for 5 mins to allow the stain to penetrate the pollen grains.
8. Remove and place the slide in a fridge or somewhere cool until the jelly has fully set.
9. Ring the coverslips with nail varnish to create a semi-permanent pollen slide.
10. Label the slide with the name of the plant and the date the pollen was collected. The date the slide was prepared may also be useful to include.
Analysing the Pollen Grains
The size of the pollen grains can be measured using a calibrated camera or by using an eyepiece graticule. Different designs of graticule exist however, the simplest form employing a measure line is sufficient. To calibrate the measure line it is necessary to use a stage micrometer and determine the value on the graticle that corresponds to an accurate measurement on the stage micrometer. By dividing the known measurement by the corresponding graticle value a calibration value is calculated at each lens magnification.
e.g. using the MUBKA compound microscope with the 0.1 mm (100 um) stage micrometer:
x10 mag 100/2.4 = 41.7 um for every graticle mark
x20 mag 100/4.8 = 20.8 um for every graticle mark
x40 mag 100/9.6 = 10.4 um for every graticle mark
Stained Hawthorne pollen grains are shown in this image. At x40 magnification this grain covered 3.8 graticle marks at its widest point. By multiplying the calibration value (10.4) by 3.8 the real size 39.5 um can be determined.
Plant Pollens
Apple Tree
Blueberry