310 PRINCIPLES OF SOIL MICROBIOLOGY 



the form of ammonia. Non-nitrogenous organic matter does not exert 

 such a depressing effect upon ammonia accumulation as in the case of 

 bacteria and other fungi; as a matter of fact, ammonia formation from 

 proteins will take place even in the presence of available carbohydrates, 

 as pointed out above. 



The accumulation of "humus" in the soil is an index of the great 

 resistance of this group of organic substances to decomposition by 

 microorganisms. Since this substance contains the larger part of 

 the soil nitrogen, its decomposition is of great importance to soil fer- 

 tility. Actinomyces seem to be among the very few organisms capable 

 of attacking this resistant material and bring about its decomposition. 

 Liming of soil and draining of swampy soil favors the development of 

 actinomyces and also the decomposition of the soil organic matter. 

 It is possible that a definite connection exists between these two phenom- 

 ena. According to Fousek an increase in plant growth is obtained by 

 adding actinomyces mycelium to soil, due to the increased decomposition 

 of the organic matter thus brought about. 



We find, among the actinomyces, organisms causing important plant 

 diseases, of which potato scab and sugar beet scab 65 are known. There 

 is considerable evidence that actinomyces may enter into certain asso- 

 ciations with plants, as pointed out by Peklo, 66 who cultivated an or- 

 ganism, named A. alni, out of the nodules on the roots of Alnus and 

 Myrica. Similar results were obtained by Lieske. In view of the fact 

 that it has not as yet been possible to obtain the nodules by artificial 

 inoculation, these results cannot be accepted as positive. 



66 Kruger, F. Untersuchungen liber den Gtirtelschorf derZuckerruben. Arb. 

 Biol. Anst. L. Forstwirt., 4: 254-318. 1905. 



66 Peklo, J. Die pflanzlichen Aktinomykosen. Centrbl. Bakt. II, 27: 451- 

 479. 1910. 



