EVOLUTION OF CARBON DIOXIDE 



187 



The formation of carbon dioxide about plant roots, whatever its 

 origin, is particularly important in plant development in that its 

 solvent action is one of the principal agencies responsible for the 

 solution of relatively insoluble soil minerals containing phos- 

 phorus, potassium, calcium, and magnesium. The development of 



30 r- 



—> ^ i-i-H -^rtroro^ —• ^ CO m ^ 



Period of Growth (Days) 



Fig. 71. — Influence of plant development upon the evolution from the soil of 



carbon dioxide of microbial origin; V — height of vegetative development, 



B — blooming, Dg — degeneration, D — death (after Starkey). 



organisms on the roots greatly increases this corrosive action, and 

 is a very important factor in determining the feeding power of 

 plants. There appear to be certain factors, not correlated with 

 either the extent of the root system or the amount of carbon diox- 

 ide produced, which determine the ability of plants to absorb 

 certain proportions of the various nutrients, at least where the 

 plants are dependent upon relatively soluble sources of inorganic 



