Kohler, R. E. Subspecies classification and biological survey, 1850s-1930s: Robert E. Kohler. Spaces of classification.(2003).
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रKohler, Robert E. "Subspecies Classification and Biological Survey, 1850s-1930s: Robert E. Kohler." Spaces of Classification.(2003) .
एमएलए (8वां संस्करण) प्रशस्ति पत्रKohler, Robert E. "Subspecies Classification and Biological Survey, 1850s-1930s: Robert E. Kohler." Spaces of Classification.(2003), .
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