238 PRINCIPLES OF SOIL MICROBIOLOGY 



These were either limited to the isolation of a few forms for bio- 

 chemical purposes, or they dealt with an important group of soil organ- 

 isms like the Mucors, 10 or with representatives of various groups in the 

 study of one important soil process, like nitrogen fixation 11 or cellulose 

 decomposition. 12 ' 13 A number of papers and monographs are available 

 which are devoted to certain groups of fungi, some of which were not 

 isolated from the soil although they are of common occurrence in the 

 soil. These contributions are of much assistance in the study and iden- 

 tification of the soil forms. Reference must be made here to the work of 

 Wehmer 14 and Thorn 15 on the genus Aspergillus; of Thorn, 16 Westling, 17 

 Sopp 18 and Biourge 19 on Penicillium; of Hanzawa 20 on Rhizopus; of 

 Butler 21 on Pythium; of Chivers 22 on Chaetomium; of Sherbakoff 23 on 

 Fusarium; and of Berkhout 24 on Monilia and allied forms. 



The composition of the fungus flora of the soil changes with a change 

 in the nature of the soil, both quantitatively and qualitatively. Hagem, 



10 Povah, A. H. W. A critical study of certain species of Mucor. Bull. Tor- 

 rey. Bot. Club, 44: 241-259, 287-313. 1917. 

 "Goddard, 1913 (p. 259). 



12 Daszewska, 1913 (p. 265). 



13 Traaen, A. E. Untersuchungen iiber Bodenpilze aus Norwegen. Nyt. 

 Magaz. Naturw. Christiania, 52: 21-121. 1914. 



14 Wehmer, C. Die Pilzgattung Aspergillus. Geneve. 1901 ; Morphologie 

 und Systematik der Familie der Aspergillaceen. Lafar's Handb. Techn. Mykol. 

 4: 192-238. 1905-7. 



16 Thorn, C. and Church, M. B. The Aspergilli. The Williams & Wilkins 

 Co., Baltimore, Md. 1926. 



16 Thom, C. Cultural studies of species of Penicillium. U. S. Dept. Agr. 

 Bur. Anim. Indus. Bui. 118, 1910; also Mycologia, 7: 134-142. 1915. 



17 Westling, R. Uber die grunen Species der Gattung Penicillium. Inaug. 

 Dissert. Upssala. Ark. Bot., 11: 1-156. 1911. 



18 Sopp, J. O. Monographic der Pilzgruppe Penicillium. Vidensk. Selskr. 

 I. Mat. Naturv. Kl., No. 11, Kristiania. 1912. 



19 Biourge, Ph. Les moississures du groupe Penicillium Link. La cellule. 

 33: 1st. fasc. 1923. Louvain. 



20 Hanzawa, J. Studien uber einige Rhizopus Arten. Mycol. Centrbl., 1: 

 406^09. 1912; 5: 230. 1915. 



21 Butler, E. J. An account of the genus Pythium and some Chytridiaceae. 

 Mem. Dept. Agr. India, Bot. Ser. 5, 1: 1-160. 1907. 



22 Chivers, A. H. A monograph on the genera Chaetomium and Ascotricha. 

 Mem. Torrey Bot. Club, 14: 155-240. 1915. 



23 Sherbakoff, C. D. Fusaria of potatoes. Cornell Univ. Agr. Exp. Sta. Mem., 

 6: 85-270. 1915. 



24 Berkhout, C. M. De Schimmelgeslachten Monilia, Oidium, Oospora en 

 Torula. Diss. Univ. Utrecht. 1923. 



