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Barker had learned microbiology from Cornelis B. van Niel at the Hopkins Marine Station of Stanford University. Van Niel had worked as Kluyver's assistant at Delft. Barker had also spent a postdoctoral year in Kluyver's laboratory before obtaining a teaching job at Berkeley in 1936.

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Scientific Genealogy of Microbial Biochemists

Martinus W. Beijerinck

Martinus W. Beijerinck (1851-1931)
Professor of Microbiology, Technical School in Delft, The Netherlands

Albert J. Kluyver

Albert J. Kluyver (1888-1956)
Beijerinck's successor at Delft

Cornelis B. van Niel

Cornelis B. van Niel (1897-1985)
Hopkins Marine Station, Stanford University, Pacific Grove

Horace A. Barker (1907-2000)

Horace A. Barker (1907-2000)
Department of Biochemistry, University of California, Berkeley

Earl and Thressa Stadtman

Earl R. Stadtman (b. 1919) and Thressa C. Stadtman (b. 1920)
Laboratory of Biochemistry,
NHLBI, Bethesda