to different wavelengths (or colors of light). He added the oxygen seeking bacteria B. termo to this setup and noted where they accumulated (Note: Four years later, Hauser concluded that B. termo had been mislabeled and was not one, but three species of bacteria of the genus Proteus ). Their clumping allowed him to see which regions had the highest concentration of oxygen. He concluded that the most photosynthetically active regions will have the highest concentrations of bacteria. The bacteria accumulated in the regions of red and violet light, showing that these wavelengths of light generated the most photosynthetic activity. However, his experiment was somewhat flawed because he used the sun as his light source. He failed to account for the fact that the sun does not emit all visible wavelengths of light at the same intensity. However, further analysis of plant pigments proved that his results were valid. A year later Engelmann discovered that purple bacteria utilise ultraviolet light in the same way. Moreover, he was among the first scientists who traced a relationship between the availability of wavelengths in underwater light (which are changing/decreasing with depth) and the occurrence of those phototrophs which can efficiently absorb and use them. Musical significance Johannes Brahms dedicated his String Quartet No. 3 to Engelmann, an amateur cellist who had hosted him on a visit to Utrecht. References External links Short biography, bibliography, and links on digitized sources in the Virtual Laboratory of the Max Planck Institute for the History of Science Original Source for Action Spectrum Experiment Bacterial Method Timeline of Photosynthesis Contributions of Theodor Wilhelm Engelmann on phototaxis, chemotaxis and photosynthesis B. termo Information 1843 births 1909 deaths 19th-century German botanists German physiologists Academic staff of the Humboldt University of Berlin Members of the Lincean Academy Members of the Royal Netherlands Academy of Arts and Sciences Leipzig University alumni Academic staff of Utrecht University Scientists from Leipzig