Letter to the Editor
archaic, old, newer, or newest lenses; in all cases, the optical outcome will be improved. Te astronomy filters used for our experiments are an
advanced and rather new optical development. Designed as modern interference filters, they are optimized with regard to their optical design. Teir transmission band is very narrow, the amplitude of the transmitted wavelengths is maximized, and the transmission of aberrant light spectra is minimized. Any reflection of light is minimized by an anti-reflection coating consisting of seven different layers. Because of their particular properties, these filters are advanced and high-tech. “A century and a half” ago such filters were not available. Might it be possible that Mr. Sterrenburg does not know the difference between such high-tech filters and simple colorized glass plates? Regarding the diatoms we used, the schematic in Figure 2
of our article was used to show morphological considerations. Te image taken at the highest magnification demonstrated that perforated and non-perforated zones indeed exist (this was not a product of our imagination). Te image in Figure 1 below shows this morphology in a high-resolution scanning electron microscopy image. It is clear to see that the repetitive non-perforated stripes in Amphipleura pellucida are broader than the perforated linear patterns. Tis situation was shown in our drawing. Our article deals with technical methods; it does not deal with the particular aspects of the morphological variance in diatom shells. Tus, it can be regarded as adequate that we showed the situation graphically for one of the specimens. In logical accordance with the highly resolved real
structure shown in Figure 1, the position of visible dark and white stripes was similar in all diatom specimens in our light microscopy observations. We could not see any “modulation” of their appearance associated with the plane of focus. When Mr. Sterrenburg describes a different appearance determined by focusing, it can be expected that this effect was caused by diffraction, that is, by an imaging artifact. Tus, Figure 1 here should verify that our explanations with regard to the morphological structures are not “completely mistaken” and “erroneous” as suggested by Mr. Sterrenburg.
Te preparations used for our evaluations were selected
by Mr. Chmela, who is a biologist. He intentionally chose very low-contrasted pieces that were just barely visible in standard white light (so-called “problem-specimens”). In these preparations the existing perforations were indeed invisible for all light microscopy techniques carried out (bright field, dark field, phase contrast, interference contrast, polarized light). We do not think that the optical equipment used by Mr. Sterrenburg is better than our equipment manufactured by Zeiss and Leitz/Leica. When Mr. Sterrenburg shows us a diatom shell resolved
better but taken in unfiltered white light with historic equipment, it is possible that the native contrast in his preparation could be much higher than in those selected for our evaluations. Te refractive index of the embedding medium is fundamental for the contrast and clarity of such low-density, unstained specimens. We do not know which kind of embedding medium was used by Mr. Göke for preparing our slides. Unfortunately, Mr. Göke has been deceased for several years so that we cannot ask him for further information. Tus, it might be possible that the preparation used by Mr. Sterrenburg was prepared with a “better” embedding medium so that more details are visible in normal circumstances. When reading Mr. Sterrenburg's letter, we can learn that
he “cannot remember having seen such an exceedingly poor illustration” of Surirella (=Petrodictyon) gemma—“even in 60 years of diatom studies.” Tis sounds rather arrogant—at least in our ears. Because of this statement, we did a short web-based research about Mr. Sterrenburg's activities. We found an article from him published in 2005 [2] containing just a few photomicrographs from diatoms arranged in a table. Tese images are indistinct, and in our personal opinion, such “poor” material should not be published. Finally, we learn that taxonomy seems to be one of
Mr. Sterrenburg's favorite “hobbies.” Several articles of his published deal with this topic. Our article was not a taxonomic article, but solely a technical contribution. Even so we feel the need to provide a last short remark concerning the names of the specimens. We used the names written onto the slides by the preparator, Mr. Göke. To make the points in our article, it was not relevant whether Surirella gemma had been renamed Petrodictyon gemma, or not. It was also not relevant for us whether this renaming took place “yesterday” or “20 years ago.” Moreover, the “old” name “Surirella” is neither “wrong” nor “illegal.” Te “new” name resulted from a diversification of the parent species “Surirella.” Nevertheless, the “old” name “Surirella” is widely used and well known. Tus, for this reason also, the criticism from Mr. Sterrenburg is not relevant for our article and our technical messages.
Acknowledgment We thank Mr. Peter Höbel, Germany, for his allowance in using his high-resolution diatom images.
Figure 1: Amphipleura pellucida imaged in the scanning electron microscope. Alternating stripes, with and without perforations, can be clearly seen (photograph by Peter Höbel, web source:
www.mikroskopie-ph.de).
2011 July •
www.microscopy-today.com
References [1] CE Lyman, Microscopy Today, 18 (5) (2010) 32–37. [2] FAS Sterrenburg, Proceedings of the California Academy of Sciences, 50(14) (2005) 156–61.
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