The vitality and germination of seeds Duvel, J. W. T. creator text book Washington Govt. Print. Off 1904 1904
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ENG Germination Seeds SB117 .D983 United States. Dept. of Agriculture. Bureau of Plant Industry. Bulletin, no. 58 https://www.biodiversitylibrary.org/bibliography/35433 12192851 agr09000191 10.5962/bhl.title.35433 Library, U.S. Dept. of Agriculture