Pennsylvania Horticultural Society. Yearbook of the Pennsylvania Horticultural Society. Pennsylvania Horticultural Society.
Chicago-referens (17:e uppl.)Pennsylvania Horticultural Society. Yearbook of the Pennsylvania Horticultural Society. Philadelphia, Pa.: Pennsylvania Horticultural Society.
MLA-referens (8:e uppl.)Pennsylvania Horticultural Society. Yearbook of the Pennsylvania Horticultural Society. Pennsylvania Horticultural Society.
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