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Optical Phenomena in Diatoms Richard B Journal of the Arkansas Academy of Science Volume 24 Article 6 1970 Optical Phenomena in Diatoms Richard B. Hoover Marshall Space Flight Center Miriam J. Hoover Cummings Research Park Follow this and additional works at: http://scholarworks.uark.edu/jaas Part of the Optics Commons Recommended Citation Hoover, Richard B. and Hoover, Miriam J. (1970) "Optical Phenomena in Diatoms," Journal of the Arkansas Academy of Science: Vol. 24 , Article 6. Available at: http://scholarworks.uark.edu/jaas/vol24/iss1/6 This article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able to read, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking prior permission from the publisher or the author. This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academy of Science by an authorized editor of ScholarWorks@UARK. For more information, please contact [email protected], [email protected]. Journal of the Arkansas Academy of Science, Vol. 24 [1970], Art. 6 (ozark) was clear, spring-fed and alkaline with a steep Creek supported a mean standing crop of 726 organ- 2 gradient. Big Creek (deltaic) was turbid, low in alkalin- isms/M . Only 55 taxa were identified, oligochaetes and ity, with slight gradient and low stream velocity. Mean chironomids dominating. These streams exhibited two standing crop for Janes Creek was 265 organisms/M*. distinct habitats due to differences in substrate, water One hundred taxa were identified, snails dominating. Big shed and land use. Optical Phenomena in Diatoms by Richard B. Hoover, Applied Physics Branch, Technology Division Geo. C. Marshall Space Flight Center, Marshall Space Flight Center, Alabama and Miriam J. Hoover, Lockheed Missiles and Space Company, Huntsville Research and Engineering Center, Huntsville Research Park, Huntsville, Alabama ABSTRACT valves (resembling a hat box). As the diatom grows, these two valves can slide apart, thereby permitting algae Diatoms are unicellular which fabricate sili- some expansion of this otherwise rigid quartz structure. ceous are frequently marked with intricate shells that The two diatom valves are frequently connected by a ornamentations and patterns. The nature and character- girdle-like (intercalary band). provide band When viewed from the istics of the siliceous shells a basis for diatom top (valve view), the shape of the diatom varies widely; give interesting taxonomy and rise to a number of and when viewed from the side (girdle view), diatoms are optical phenomena. paper presents colorful This the generally rectangular. Diatoms are usually divided into results of investigations of diffraction phenomena, com- two orders; comprising radially sym- opti- the Centrales the plementary color behavior, Rayleigh scattering and metric diatoms and the Pennales comprising bilaterally cal activity in diatoms. symmetric and asymmetric diatoms, as seen in valve view. Many of the Pennate diatoms possess a V-shaped 1. INTRODUCTION groove (raphe) in the valve wall. By exuding cytoplasm collecting again Diatoms are a distinct group of unicellular algae be- along this raphe, and it at a central or nodule, propel through longing to the phylum Chrysophyta and the family Bacil- polar the diatom can itself the 2 3 Only raphe lariophyceae. Alldiatoms characteristically encase them- water . diatoms with a true have the power in (frustules) composed of extremely of locomotion; all others are either free floating or at- selves cell walls objects. pure hydrated amorphous silica (i.e., silicic acid as a tached to aquatic plants or other underwater polymer). Chemical analysis of the frustules of marine The surfaces of diatom shells or frustules often ex- planktonic diatoms indicated 96.5% SiO 2 and approxi- hibit complex and intricate ornamentations. These usual- mately 1.5% of AI2O3 and 1.5% Fe 2O3.' Diatom shells ly consist of thickened ribs arranged in a fairly definite have a refractive index of 1.43. pattern, hyaline areas, spikes, alveoli, costae and fine The diatom shell is constructed of two overlapping (2) Cornelius Onderdonk, The Microscope, August, 1890. (1) "Silicification" by Joyce C. Lewin in Physiology (3) Ruth Patrick and Charles W. Reimer, The Di- and Biochemistry of Algae, Academic Press, New York, atoms of The United States, Vol. 1., Academy of Natural New York (1962), p. 448. Sciences of Philadelphia, 1966, pp. 22-23. Published by Arkansas Academy of Science, 1970 8 1 Journal of the Arkansas Academy of Science, Vol. 24 [1970], Art. 6 • orange or yellow.* This lines or striae. The nature and characteristics of these mitted light is turbid occurs ornamentations and the structure of the siliceous shell because the pores are large enough to scatter the a basis for diatom taxonomy. They also give short wavelengths but too small to deviate the longer nrovide _i :_x i.:__ __i__r..i >:__i i i Irise to a number of interesting and colorful optical waves which are consequently transmitted. Due to Ray- phenomena. 4 Many of these effects are well under- leigh scattering, Heliopelta appear bright blue with a stood, while others await explanation. bronze maltese cross in the center surrounded by a crown of golden spikes. 7 II. DIFFRACTION PHENOMENA INDIATOMS This technique has been used to detect the pre- subwavelength pores Navicula, diffraction colors may be observed by il- sence of diameter in Beautiful Nitzschia, Pleurosigma, Gyrosigma, Stauroneis, Pleuro- luminating a spray of diatoms which possess straight stauron, Actionoptychus, Actinocyclus, etc. It is a striae (e.g., Navicula, Nitzschia, Pinnularia, etc.) and parallel valuable tool it provides useful information an intense unidirectional white light source. The because with about the microstructure of the cell wall. diatoms oriented such that these striae are perpendi- cular to the direction of the light will behave as small diffraction gratings and produce brilliant colors.3 The IV. OPTICAL ACTIVITY IN DIATOMS entire range of the spectrum is obtainable and the hue Since the diatom cell wall is hydrated amorphous will change markedly with small variations in the angle silica, it is generally assumed that diatoms would have of illumination. These colors disappear in uniform light no effect on the state of polarization cf visible light. and are not visible with a large aperture objective or During this work, over a thousand species of diatoms with a wide illuminating cone. were examined and only a few were found to have any effect on the state of polarization of visible light. Diffraction colors are only observable if the illuminat- ing is in the proper azimuth and are best seen beam These include: against a dark background. The colors will disappear if the system is rendered optically homogeneous by using 1. A specimen Aulacodiscus Oregonus from Santa a mounting medium of the same refractive index as the Maria, California which glows a brilliant yellow when diatoms. viewed through crossed polarizers. 8 2. Pleurosigma Angulatum from the United States III. RAYLEIGH SCATTERING as well as from Hawksbury, Australia, has been found bright polarizers. Many diatoms contain pores, poroids or fissures in to exhibit blue colors under crossed two specimens overlap, the cell wall which are so small that they may not be Where a color shift may occur directly light microscope. However, and shades of red and pink have been observed and seen with the visible photographed. may organic their presence may by observing diatom This be caused by material be detected the remaining specimen.* in dark field illumination. If the transparent particles or in the pores of the diatom are larger than 1 micron diameter, the diatom will appear white under dark field illumina- (6) The photograph of Actinoptychus heliopelta pub- tion. Diatoms belonging to the Genus Triceratium, Cos- lished in Physics Today, p. 24, December 1970, shows cinodiscus, Synedra, Pinnularia, Melosira, Stictodiscus, the brilliantTyndall blue arising from Rayleigh scattering Hyalodiscus, Fragillaria and many others behave in this at small pores in the diatom frustule. The unscattered radiation forms a gold maltese cross in the center of the diatom and a golden periphery. If the diatom contains transparent pores which (7) The Tyndall blue can also be seen in the spray approximately 0.3 microns in diameter, the scatter- of Heliopelta, McGraw-Hill Encyclopedia of Science and light will be a brilliant Tyndall blue and the trans- Technology, 1971 Edition, (Photograph g). (The subtle I spikes colorations of the central cross and cannot be seen in this reproduction.) The actual pores forming the During this research, several thousand color pho- striae can be seen in the oil immersion photomicrograph icrographs were produced, which clearly illustrate of Actinocyclus Ellipticus (McGraw-Hill Encyclopedia of e phenomena. Many of these photographs have al- Science and Technology - Photograph i). ly appeared in full color in a wide variety of publi- (8) Photomicrographs showing optical activity in this 3ns. These willbe referenced to permit the reader to diatom have been published in color by the Dicalite Di- 1(4)Jrve interesting phenomena. Grefco, publications in these color vision of Inc. Some of the which (5) Diffraction colors are illustrated in the spray of this photograph may be found include: Chemical Week, diatoms from Pensacola, Fla., which will appear in the May 6, 1970, p. 20; Chemical and Engineering News, color plate "Diatoms," to be published in the McGraw- May 11, 1970; Filtration Engineering, May 1970; Chemi- HillEncyclopedia of Science and Technology, 1971 Edi- cal Engineering Deskbook, April 27, 1970. tion. The diagonally oriented Navicula lyra and Nitz- (9) A photomicrograph of a spray of Pleurosigma schia sp. are a brilliant yellow whereas those oriented (produced by another researcher) appears on the cover horizontally are a deep reddish orange (Photograph b).
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