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- Adelaide Botanic Gardens.
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- Adolph Fischer Nurseries.
- Adolph, Clement
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- Adolphus Wysong (Firm)
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- Adrian J. Schoorl (Firm)
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- Advance Dahlia Gardens.
- Advance Seed Company.
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- Aeronautical Research Associates of Princeton.
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- Afonso, Luis Orlando Bertola
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- Afonso, Marisa C
- Afonso-Carrillo, Julio
- Afriastini, Johar Juniati,
- African Bird Club.
- African Conservation Fund and Uaso Ngiro Baboon Project
- African Expedition of the American Museum of Natural History (1912-1913)
- African Research Survey.
- African Violet Nursery,
- African Violet Society of America.
- Afshan, Najam-Ul-Sahar
- Afshar-Harb, Abbas
- Afshari, Fatemehi
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- Agassiz Association. Department of the Wilson Chapter.
- Agassiz Association. Wilson Ornithological Chapter.
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