Diatoms are single-celled algae. Since they are smaller than 1 mm, they can only be seen with the aid of a microscope. They live abundantly in lakes, streams, and oceans and exist even in wet habitats as tiny as the bark of a tree. The number of different diatom species, that is their biodiversity, is estimated at 1 million, with only 20,000 species having been described. The ecological significance of these organisms becomes enormous, if you take notice of diatoms producing about 25% of the global oxygen.
But apart from the scientific aspects, they are intriguing to look at: Their glass shells are incomparably beautiful and their pronounced symmetry fascinates the observer. The exhibition is divided into three parts: art, documentation, and science.
Starting in the 19th century, diatoms became a popular subject of study among (many) amateurs and (few) scientists. The preparation and arrangement of these small algae into orderly rows, circles, and other elaborate patterns was usually the work of amateurs. Johann Dietrich Möller (1844-1907) perfected the skill of arranging diatoms into such arrays on microscope slides. While he made a living by selling these slides, it was also important to him to have his works published among experts. In the exhibition large-size prints of modern micro-photos illustrate the diversity of diatoms in the microscopic slides from the 19th century. The exhibition will display slides prepared by Möller, Eduard Thum, and Henry Dalton.
The creativity displayed in the microscopic slides ranges from mathematical symmetries up to mosaic-shaped arrangements of bouquets, butterflies, and birds. By using different microscopy techniques, the same product can (in dark-field transmitted light or in reflected light) become two very different works of art: manifold colors unfold by light refraction at the diatom shells. The production technique of the historical specimens is illustrated by a photo from 1891 of J.D. Moller's workplace.
The largest microscope slide of this kind was prepared in 1891 and is called "The Universe" by J. D. Möller. On one slide sized 5x6 mm, more than 4000 different diatom species are arranged into even and uniform rows. A printed catalog identifies every single species and its exact position on the plate.
The purely morphologically based classification, the basis of the historic "Universe" slide, is compared to a modern phylogenetic tree that builds on the knowledge of centuries of molecular and finely structured analysis of diatoms for a modern synthesis. At a media station visitors will be able to interactively question the historical "Universum" and look up the current state of each algae in the information system for terrestrial and freshwater microalgae, AlgaTerra (www.algaterra.org).
Electron microscope pictures of the ultrastucture of diatom shells illustrate recent international research findings, including findings by the diatom group at the Botanic Garden and Botanical Museum Berlin-Dahlem (BGBM).