THE ETCHING OF MARBLE BY ROOTS IN THE PRESENCE 

 AND ABSENCE OF BACTERIA.* 



By E. B. FRED and A. R. C. HAAS. 



{From the Department of Agricultural Bacteriology, University of Wisconsin, 



Madison) 



(Received for publication, April 22, 1919.) 



In studies on plant nutrition^ it is essential to investigate the re- 

 ciprocal effects of the plant and of the soil bacteria upon one an- 

 other. In a recent paper^ the writers have shown that germinating 

 legume seeds do not excrete substances in quantities sufficient to 

 exert a toxic action upon the growth of the nodule bacteria of such 

 plants. The present report makes it evident that soil bacteria may- 

 play an important part in the nutrition of plants. 



It is a well known fact that roots in the presence of bacteria have 

 the power to carry on active solution processes and thereby increase 

 the available plant food in the soil. The means by which such a dis- 

 solving action of minerals takes place is a matter of considerable im- 

 portance.^ Unfortunately the problem has been complicated* by the 

 failure of many investigators^ to distinguish clearly^ the factors^ 

 that are involved. Some interesting observations as to the causes 

 for soil acidity have recently been made.^-^ 



That the acid excretion from roots has the power to etch marble 

 has long been known. This power of roots to dissolve marble be- 



* Published with the permission of the Director of the Wisconsin Agricultural 

 Experiment Station. 



^Lyon, T. L., J. Am. Soc. Agron., 1918, x, 313. 



^ Haas, A. R. C, and Fred, E. B., Soil Science, (in press). 



3 Haas, A. R., Proc. Nat. Acad. Sc, 1916, ii, 561. 



4 Crocker, W., Bot. Gaz., 1917, bdii, 422. 



^ Czapek, F., Biochemie der Pflanzen, Jena, 1905, ii, 869, 

 ^ Kappen, H., Landw. Vers. Sta., 1918, xci, 1. 

 7 Johnson, H. V., Am. J. Bot., 1915, ii, 250. 

 ^Hoagland, D. R., Science, 1918, xlviii, 422. 



9 GiUespie, L. J., and Wise, L. E., /. Am. Chem. Soc, 1918, xl, 796. 



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