A perfect sample for understanding the fine focus procedure: Pollen grains from Cobaea scandens

Cobaea Scandens (Jacob’s ladder family) is a widespread ornamental plant for garden and balcony. Domiciled in Mexico, this climbing plant is cultivated as an annual in the temperate zones.

Beside its aesthetics with bell-shaped violet flowers, there are two more aspects worth to mention:

• This plant is pollinated by bats. 
• Tthe large (~ 160 microns Ø) pollen grains of Cobaea show a complex structure which is worth to discover.

Pollen Grains in Brighfield

To give a full description, we should reactivate our Greek and Latin lessons from school:

Panto (from Greek: pan) = all, all over. And aperture (from Latin: apertura) = opening.

Cobaea pollen belongs to the “panto-aperturate” pollen class with openings for the pollen tube spread all over its surface. Further, the outer “skin”, the “exine”, shows a reticulate structure based on small rods. The pollen surface looks a little bit like a fine- patterned football.

To discover the full beauty of this pollen, we have to perform the “acetolysis”, a chemical treatment using acetic anhydride and sulfuric acid to increase the transparency of the pollen grains. For further details please refer to: 

  

"Leitfaden der Pollenbestimmung: 

für Mitteleuropa und angrenzende Gebiete"

Hans-Jürgen Beug

ISBN: 978-3899370430

"Pollen analysis"

Peter D. Moore

ISBN: 978-0865428959

We cannot compete with the images taken by a Scanning Electron Microscope, as in this case the depth of view is endless, but a good usage of our light microscope also gives a remarkable insight.

©https://www.paldat.org/search/genus/Cobaea 

The “inner surface” of the pollen grain shows the predefined apertures for the germination of the pollen tubes, while the optical “cross section” of the pollen grain displays the rods in longitudinal view.

Predefined pores for pollen tube germination

Rods in longitudinal section

Only by using very precisely the fine focus, the different height levels can be piloted. One more time the knowingly usage of a standard light microscope discovers structures which seemed to be not accessible to such a “simple” instrument.

Thanks to Klaus Laumeier, Cologne, Germany for the preparation of recent material