MICROORGANISMS AS A FACTOR IN SOIL FERTILITY 303 



media. As to the numbers and types in relation to depth, Goddard 

 concluded that there does not seem to be any appreciable variation in 

 numbers at the different soij depths. Unpublished data of the New 

 Jersey Experiment Station bring out the fa,ct that there are very few 

 fungi in the soil below 8 inches, and that one of the most common forms 

 at these depths is ZygorrhynchurS vuilleminii. It was formerly thought 

 that soil fungi are abundant only in acid soils, but recpnt investigations 

 make it appear that also limed and well-cultivated soils have an 

 abundant fungus flora. 



Ammonification. — Mvintz and Condon, and after them Marchal, 

 working with pure cultures, proved conclusively that fungi decompose 

 organic matter and cause an accumulation of ammonia in the soil. 

 Wilson and McLean iound that the forms of MoniUaene the most active 

 ammonifiers among the several groups of organisms studied, while the 

 Aspergilli showed the least ammonifying power. More recent work 

 has confirmed the earlier findings and has proved that fungi may 

 play an active part in the decomposition of organic matter, and the 

 accumulation of ammonia. 



Nitrogen-fixation. — Experiments on nitrogen-fixation by fungi were 

 carried on by Jodin as early as 1862. He observed a rich fungus growth 

 on nitrogen-free media, supplied with sugary tartaric acid, or glycerin. 

 Berthelot, Saida, Ternetz, and others also reported fixation of atmos- 

 pheric nitrogen through the activities of fungi, such as Aspergillus 

 niger, Altemaria tenuis and several species of Monilia, Penicillium, 

 Mucorini and others. But other investigators among them, Wino- 

 gradsky, Czapek and Heinze were unable to confirm these observa- 

 tions. The careful .work of Goddard has also given negative results. 

 The entire question is therefore still an open one with the weight of 

 evidence on the negative side. 



Cellulose Decomposition. — The destruction of cellulose in the soil is 

 due t.o a large extent, to the activities of soil fungi, as has been demon- 

 strated by several investigators. Cellulose decomposition by fungi was 

 first observed in the study of plant diseases. Van Iterson used filter 

 paper for the isolation of fungi, by exposing this medium to the air for 

 twelve hours. Thirty-five species of fungi were isolated thus proving 

 that a large number of cellulose-destroying fungi may be present in 

 the air. Appel found that certain species of Fusarium destroyed in 

 fourteen days 80 per cent of the filter paper used. Marshall Ward 



