CARBON AND NITROGEN CYCLES IN THE SOIL 217 



TABLE LVI. NUMBERS OF ACTIVE BACTERIA AND SPORES OCCURRING IN 

 SOILS AND CAPABLE OF GROWTH ON GELATIN PLATES. RUSSELL AND 

 HUTCHINSON (24ic). MILLIONS PER GRAM OF DRY SOIL. 



The active forms must be held responsible for some at 

 least of the oxygen absorption, carbon dioxide evolution and 

 decomposition going on. Under comparable soil conditions a 

 distinct relationship exists between the productiveness of the 

 soil and the amount of bacterial activity, although it cannot 

 be expressed in any definite form. Counts of the numbers of 

 bacteria by any particular method fail to give results sharply 

 connected with productiveness (although there is a general 

 relationship) because the organisms are of the most varied 

 description (ill), and of widely different efficiency as food 

 makers. Nor, on the other hand, have the methods of physi- 

 ological grouping helped much, since they necessitate growth 

 in culture media wholly different from the soil under tempera- 

 ture and water conditions that never obtain in nature. Not 

 until the fundamental difficulty has been overcome of syn- 

 thesising a soil identical with natural soil will it be possible 

 fully to interpret the many interesting observations that soil 

 bacteriologists are now accumulating. The subject is further 

 discussed in Chap. VII. 



