DEVELOPMENT AND ACTIVITIES OF ROOTS OF 



CROP PLANTS. 



A STUDY IN CROP ECOLOGY. 



BY 



John E. Weaver, 



Professor of Plant Ecology in the University of Nebraska, 



Frank C. Jean, 

 Professor of Botany in the Peru (Nebraska) State Normal School, 



and 



John W. Crist, 

 Instructor in Botany in the University of Nebraska. 



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