48 



It is obvious that aeration will effeot importantly 

 the nitrogen cycle in the soil. Doubtless additional 

 effects follow the encouragement of putrifactive and 

 other anaerobic organisms by deficient aeration. 

 These may be especially important in the complex reac- 

 tions involved in humus formation. The toxins which 

 are probably excreted by higher plants under anaerobic 

 conditions have already been mentioned. 



l. On putrifaction and fermentation in soils 

 see: Kossowicz, loc . cit . ; Sorauer,- Handbuch Pflanzen 

 krankh. vol. 1, pp. (1886); Wacker,- Jahrb. wiss. Bot. 

 32: 71-116 (1898). On toxic excreta of bacteria see Dan- 

 deno,- Report Mich. Acad. Sci. 10: 32-36 (1908). 



2. See V/ollny,- Jour. Landw. 34: 213-230 (1886), 

 Der Zersetzung der organischen Stoffe, pp. 140ff, (1897); 

 Sjollema and de Ruijter de Wildt,- Verslag landbouwk 

 Onderzoek. Rijkslandbouw proefstat 1: 21-68 (1907), !_'- 

 106-146 (1910). On soil bacteria in general see Kosso- 

 wicz,- loc . cit . ; LBhnis,- Handb. landw. Bakteriol. 

 (1910); Russell,- Soil Gonds. and Plant Growth, 2nd 



ed. , pp. 117-139 (1915); Lipman in Marshall,- Micro- 

 biology, 2nd ed., pp. 289-363 (1917). 



3. See pages //*— ^L/ and literature cited on 

 page /f , note ( 



