THE CYCLES 



373 



C02 



Air, and dissolved air 



Respiration 

 Decomposition 



Organic matter of algae and 

 photoautotrophes in general 

 (chiefly in water) 



Organic matter of autrotrophic 



bacteria (chimioautotrophes) 



(chiefly in soil) 



Organic matter of 

 saprophytic micro-organisms 



Fig. 100 (after Butlin andj^Postgate) — A microbiological carbon cycle. 



