+---------------<-----------------+ | | _Dead animal | protein_ | | ^ | | v | _Free N taken <-----_Decomposition <-------------+ | up by free living bacteria_ <----------+ | | N absorbers and | | | | root tubercle | | | | bacteria_ v | | | | _NH₃ compounds | | | | in soil_ | | | | | | | | | | | | | | v | | | | _Nitrite bacteria_ | | | | | | | | | | | | | | v | | | | _Nitrites_ | | | | | | | | | | | | | | v | | | | _Nitrate bacteria_ | | | | | ^ ^ ^ | | | | | | v | | | | _Nitrates in soil_ | | | | | | | | | | | | | | v | | | | _Green plants_ | | | | | | | | | | | | | | v _Dead plant | | +------->_Plant protein_----> protein_ | | | | ^ | | | v _Animal waste, | _Animals_---------->urea, etc._ | | | | | +-------->------------------------+ FIG. 70.--Diagram to illustrate the circulation of nitrogen through the agency of bacteria.] [Illustration: