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2. Gilbert : Inaugural Lecture, University of Oxford. 



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4. Gilbert: The Scientific Principles of Agriculture (Lecture). 



5. Minnesota Agricultural Experiment Station, Bulletin No. 30. 



6. Stockbridge : Rocks and Soils. 



7. Association of Official Agricultural Chemists, Report 1898. 



8. Maryland Agricultural Experiment Station, Bulletin No. 21. 



9. Minnesota Agricultural Experiment Station, Bulletin No. 41. 



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14. Unpublished results of author. 



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1 6. Roberts : Fertility of the Land. 



17. Minnesota Agricultural Experiment Station, Bulletin No. 41. 



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25. Peter : Association of Official Agricultural Chemists, Report 

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28. Houston : Indiana Agricultural Experiment Station, Bulle- 

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