86 



carbon dioxide in increasing the solubility of minerals 

 in the soil solution and thus assisting the nutrition 

 of the plant. 



1, On the effect of carbon dioxide in increas- 

 ing the solubility of minerals see Sachsse,- Lehrb. 

 Agriculturchem. p. 181 (1888); Cameron and Bell,- U. S. 

 Bur. of Soils, Bull. 30, pp. 32-34 (1905); Engels,- landw. 

 Vers. Stat. _77: 269-304 (1912); Mettler,- Zeits. Sauer- 

 stoff und Stickstoff Indust 5: 193 (1913); l.litscherlich.w 

 Bodenkunde, 2nd ed., pp. 153, 178-187 (1913); Clarke, - 

 Data of Geochem., U. S. Geol. Survey, Bull. 616 : pp. 478- 

 486 (1916). Further literature is cited by these author^, 

 especially Cameron and Bell^ and Clarke. On the solvent 

 action of roots and of bacteria due to excreted carbon 



dioxide, see: Sachs,- Bot. Ztg. : 117 (1860) 



(This is the original observation of root-prints on a 

 marble slab, then interpreted as due to organic acids); 

 Xossovich,- Zhur. Opyt. Agron. 5: 482-493 (1904); Hall,- 

 Science Prog. 1: 51-57 (1906); Bassalik,- Zeits. fur 

 Qarungs^physiol. 2: 1-32 (1912); Pfeiffer and Blanck,- 

 Landw. Vers. Stat. 21'- 217-268 (1912); and the authori- 

 ties on excretion of carbon dioxide by roots cited on 

 page , note . On the action of carbon dio- 

 xide in modifying soil flocculation through changes in the 

 solubility of. the salts of magnesium and calcium see: 

 Ehrenberg,- Bodenkolloide, pp. 432-434 (1915). 



