. Elementary principles of agriculture : a text book for the common schools . Fig. 49. Poisonous substances in the soil, formed by decaying vegetable matter, some- times Iceep a fertile soil from being pro- ductive. fWheat seedlings grown in: (1) Pure distilled water; (2) soil extract; (3) same soil extract from wiiicii the poisonous substances have been removed by absorp- tion with carbon black.) Bureau of Soils, United States Department of Agriculture. (95)

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Keywords: ., bookcentury1900, bookdecade1910, booksubjectagriculture, bookyear