ABSOBPTIOir OF NUTRITIVE SALTS 409 



and that they are responsible, in large measure, for the 

 injurious effect on plants of a very compact condition of 

 soil. In the same communication these authors report 

 an experiment in which it was found that the kinds of 

 plants that excrete the largest quantity of carbon dioxide 

 from their roots are the ones that absorb the greatest 

 quantities of phosphorus from gneiss and from basalt. 

 This, however, does not necessarily connote any conse- 

 quential relation between these physiological functions. 



Barakov ^ drew air through planted soils contained in 

 large tanks. He found that the maximum production 

 of carbon dioxide occurred at the time when the plants 

 were blossoming, whether the plants blossomed early 

 or late in the season. This he considered to indicate 

 that the plant assists most vigorously in the solution of 

 nutrient materials at the time when it is most active in 

 absorbing them. 



325. Insufficiency of carbon dioxide. — Pfeifler and 

 Blanck ^ passed carbon dioxide through soil contained in 

 vessels in which plants were growing. The soil in some ves- 

 sels contained a difficultly soluble tricalcic phosphate, that 

 in other vessels the more easily soluble dicalcic phosphate, 

 and that in still other vessels was unfertilized. Another 

 set of vessels having the same fertilizer treatment received 

 no carbon dioxide. The soil receiving carbon dioxide 

 produced larger yields of dry matter and phosphorus in 



^1 Barakov, F. The Carbon Dioxide Content of Soils at 

 Different Periods of Plant Growth. Jour. Exp. Agr. (Russian), 

 Vol. 11, pp. 321-342. 1910. The authors are indebted to 

 Dr. J. Davidson for a translation of this paper. 



^Pfeiffer, Th., and Blanek, E. Die Saureausscheidung 

 der Wurzeln und die LosHchkeit der Bodennahrstoffe in Xoh- 

 lensaurehaltigem Wasser. Landw. Vers. Stat., Band 77, Seite 

 217-268. 1912. 



