Dandelion pollen in dark-field

Stacked image of dandelion pollen in dark field

The pollen grains from a dandelion (Taraxacum sp.) were collected and air-mounted (no liquid mounting medium used). Eleven separate images were stacked together to increase the depth of field and to produce the final image. The color contrast was then adjusted. Dark-field patch stop was used.

10 thoughts on “Dandelion pollen in dark-field”

  1. Interesting golden color. Quite nice against a black background. What magnification was this? And do you think it would have been sharper if it were in a mounting medium (that is, if you had used a 100x oil lens)? Thanks!

  2. >What magnification was this?
    I don’t quite remember, but I think I used the 10x or 20x objective.

    >And do you think it would have been sharper if it were in a mounting medium (that is, if you had used a 100x oil lens)?
    There are 2 different issues here: mounting medium or not and 100x oil immersion.
    Mounting medium, e.g. water (instead of air): I tried it, but this gives a quite different impression. The color does not appear to be as intense and the pollen look more transparent. Also: the water makes the pollen swell up.

    100x oil: This reduces the field of view massively, and there would have been the necessity to make a panorama image (stitching). The 100x oil also has a low depth of field and there would always have been some parts out of focus. So stacking would also have been necessary. To use the full numeric aperture of a 100x objective, a mounting medium (eg. water) would have been necessary and this complicates issues. The pollen float around as the water evaporates and it is very difficult (or impossible) to take same images at different levels for stacking purposes. A permanent mount would have been necessary, but the organic solvents in the mounting medium may actually dissolve the yellow pigment out. So, I should have used a water-based mounting medium such as glycerine gelatin, but this one is difficult to use (or I was to lazy….)
    100x oil is suitable for very thin specimens and the pollen is not very thin.
    Oliver.

  3. Hello Oliver,

    Oh my gosh, that was a lot more than I expected. Thank you so much for opening my eyes to so many variables to consider. Youch! Much to consider for a single photograph. I have thought about stacking images, and also stitching them afterwards into a big image. For one “single” image, it’s a lot of work. 🙂 Haha. Anyhow, thank you for the explanation.

    Take care,
    Huy

  4. I have a USB Proscope with 10X, 100X & 200X lens. I am interested in examining the pollen from the plants that grow in my area. I will use the camera feature to record each of them for my archives so I will not be collecting the specimens to save on the slide. What do you think is the best method for viewing them-magnification and process?
    I also raise bees and plan to collect pollen from their hives during the spring and summer and compare it with the plant pollen that I collect to see if I can make matches.

  5. @Ken:
    For making permanent mounts of pollen you can try:
    a. mounts (no mounting medium, only air). This works fine for low magnifications.
    b. Mount the pollen in Glycerine Gelatine (according to Kisser, not Kaiser). In this case no fixing in alcohol is needed and the shape of the pollen are preserved.
    c. Using mounting medium with an organic solvent (like Euparal). This may lead to the dehydration of the pollen, and shrinkage.

    Be aware, that plant identification based on pollen analysis is a quite complex science.
    Oliver.

  6. Would you please give me just a few more details on your mounting? Do you still use a coverslip? Do you place pollen in a well on a slide, protected with a coversip? If not, how do you prevent the pollen on the slide from getting blown around?
    Respectfully,
    John D’Errico
    Columbus, Georgia

    1. Hello,
      The pollen is first placed on a regular slide (no well, no concave slide) and a cover glass is placed directly on top. This protects the pollen and also makes sure that they are more or less level. The cover glass can then be held in place with thin strips of adhesive tape on the side. You can also try to seal the cover glass with nail polish, but the risk is quite high that some of it will flow beneath the cover glass. Use highly viscous nail polish (allow solvent to evaporate before applying). The slides should then be stored horizontally, but I found the pollen to stick well to the glass anyway. For making pollen slides with a mounting medium, you can use Glycerin Gelatin according to Kisser (not Kaiser). This is a water-based mounting medium which is compatible with the delicate pollen.
      Mounting medium is sold by many lab supply companies: http://www.serva.de/enDE/CatalogDetails/3390_184_23312_Glycerol_gelatin_after_Kisser_phenol_free.html

      Oliver

    1. Hi,
      The pollen is so small that crushing them is unlikely. This would be a problem with larger specimens. Small insects would need the support of the surrounding mounting medium. The tape does not really press the cover glass down, the force is not high, it kind of prevents it from being blown off. The tape is also on the side, while the pollen is more in the center. So I would guess that the force is not really directed at the pollen. If you have a look at the picture, you will see that some of the pollen overlap a bit, so there seems to be some space. I would try the following (having not tried it myself): Place a cover glass on top and then use a pencil (etc) to press down on the cover glass while looking through the microscope. If the pollen deforms, then this is an indicator that they are indeed crushed. But I do suppose that most pollen are rather strong anyway. Oliver.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.