256 SOIL CONDITIONS AND PLANT GROWTH 



Bouilhac l and Giustiniani 2 showed that in sand free from 

 organic matter and nitrogen compounds, soil bacteria and 

 algae not only develop normally, but also enrich the soil 

 with nitrogen sufficiently to support the growth of higher 

 plants ; while still more recently Pringsheim 3 has shown that 

 the ability of bacteria to fix nitrogen is closely dependent 

 upon the presence of blue-green algae (see p. 200). 



A third possibility discussed by Gautier and Drouin 4 is 

 that algae may assimilate ammonia or nitrate in the soil and 

 convert it into complex organic substances. The existence 

 of an action of this kind in normal soils has been indicated 

 by Russell and Richards (24 1). 



Harrison and Aiyer (126) maintain that algae serve a 

 special purpose in swamp soils, taking in CO 2 and giving 

 out oxygen, which is then available for the plant roots. 



2. Fungi. 



It has long been known that fungi occur in the soil, and as 

 long ago as 1886 no less than eleven different species were 

 isolated by Adametz. 5 Subsequent workers have greatly en- 

 larged the list and more than 200 species have now been de- 

 scribed as soil fungi. 



The investigations have fallen into several groups. Some 

 workers, as Butler 6 in India, Hagem 7 in Norway, and Lendner* 



1 R. Bouilhac, Sur la fixation de Vazote atmospherique par Vassociation 

 des algues et des bacteries (Compt. Rend., cxxiii., 1896, pp. 828-830). 



2 R. Bouilhac and Giustiniani, Sur line culture de sarrasin en presence d'un 

 melange d'algues et de bacteries (Compt. Rend., cxxxvii., 1903, pp. 1274-6). 



3 E. Pringsheim, Kulturversuche mit chlorophyllfiihrenden Mikro-organ- 

 ismen., III. Zur Physiologie der Schizophyceen (Cohns, Beitrage z. Biol. d. 

 Pflanzen, Bd. xii., pp. 99-107). 



4 Gautier and Drouin, Recherches sur la fixation de Vazote par le sol et les 

 vegetaux (Compt. Rend., cvi., 1888, pp. 754, 863, 944, 1098, 1174, 1232, 1605). 



5 L. Adametz, Untersuchungen uber die niederen Pilze der Ackerkrume 

 (Inaug. Diss., Leipzig, 1886). 



6 E. J. Butler, An Account of the Genus Pythium and some Chytridiacece 

 (Mem. Dept. Agric., India, Bot. Ser., 5, I, 1-160, 1907). 



7 O. Hagem, Untersuchungen tiber norwegische Mucorineen (Videns. Skrift, 

 I., Math. Nat. Kl., 1907, No. 7 ; Part II., 1910, No. 4). 



8 A. Lendner, Les Mucorinees de la Suisse, Berne, 1908. 



