Fungous Flora of the Soil 425 



of the presence of facultative parasites in the soil: that of growing the 

 crop under control experimentation and, provided disease arises, of 

 isolating the organism from the host in case it is of parasitic nature. Sap- 

 rophytes may likewise be isolated from the debris of plants after death 

 has occurred. 



While a number of organisms causing disease in certain crops are 

 generally recognized as living in the soil as saproph3rtes, at least for some 

 years, still we are rather prone to say such is the case without any too 

 much evidence. It cannot be emphasized too strongly that more work 

 of the nature of Busse, Peters, and Ulrich ('11), connected with the demon- 

 stration of the cause of the " Wurzelbrand " of the sugar beet and the 

 presence or absence of the causal organisms in the soil, should be under- 

 taken. A brief discussion of the history of investigations on this subject 

 is as follows: Busse and Ulrich ('08) demonstrated that beet seed-balls 

 were attacked by Phoma Betae Fr., while the two other fungi known to 

 produce " Wurzelbrand " — Pythium de Baryanum Hesse and Aphano- 

 myces laevis de Bary — could not be demonstrated in any case as occurring 

 on the seed-balls. The conclusion of their work is that the diseases 

 produced by the two latter-mentioned fungi do not take their starting 

 point from the seed. 



Kriiger ('93) came to the conclusion, as a result of his investigations, 

 that infection of beets can come from the soil. Perhaps this is not con- 

 clusive, as his communications are too general. 



Hiltner and Peters ('05) disinfected the seed-balls after the Hiltner 

 sulfuric acid method (1. c. 220). In all three soils investigated (which 

 were obtained from different sources and were of different natures), the 

 authors found that when sterilized soil, as well as sterilized seed-balls, 

 was used, some disease arose. . These results must undoubtedly be at- 

 tributed to improper sterilization, and, according to the evidence of the 

 following citation, the seed-balls could not have been sterilized. 



Busse, Peters, and Ulrich ('11) found that on complete sterilization of 

 soil and seed-balls no " Wurzelbrand " could be produced. When com- 

 pletely sterilized seed -balls but unsterilized soil were used, " Wurzelbrand " 



('93) Kriiger, F. Phoma Betae Fr. als einer der Erreger von Wurzelbrand der Riiben- 

 pflanzen. Zeitsch. Ver. Rubenzuckerind. 43: — . 1893; cited in Arb. Kais. Biol. Anst. 

 Land-, und Forstw. 6: 261. 1908. 



('05) Hiltner, L., and Peters, L. Untersuchungen iiber die Keimlingskrankheiten 

 der Zucker-. und Runkelriiben. Arb. Kais. Biol. Anst. Land-, und Forstw. 5: 207-253. 



1905- 



('08) Busse, W., and Ulrich, P. Uber das Vorkommen von Wurzelbranderregern 

 auf der Riibensaat. Arb. Kais. Biol. Anst. Land-, und Forstw. 6: 373-384. 1908. 



('11) Busse, W., Peters, L., and Ulrich, P. Uber das Vorkommen von Wurzel- 

 branderregern im Baden. Arb. Kais. Biol. Anst. Land-, und Forstw. 8: 260-302. 

 1911. 



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