:il Robert S. Kihby 



as those of the first part of the host-range test, except that five kernels of 

 No. 6 Junior wheat were planted in each pot. The twenty-five pots were 

 divided into five series of five pots each. The first series of pots received 

 no fertilizer, while each of the other four series received one of the following 



treatments : 



1. One gram of sodium nitrate per pot, applied by dissolving in 100 



cubic centimeters of water which was then poured over the soil. 



2. One-half gram of acid potassium phosphate (dibasic) per pot, mixed 



with the soil. 



3. One gram of sulfur per pot, mixed with the soil. 



4. Three grams of hydrated lime per pot, mixed with the soil. 



After seventeen weeks of growth, no marked differences were found 

 among the different series. Later, the series to which lime had been added 

 was the first on which perithecia were found. This series had more killed 

 plants (15.7 per cent) than the sodium nitrate series (13.6 per cent), the 

 acid potassium phosphate series (5 per cent), or the sulfur series (none), 

 and had less dead plants than the series to which no fertilizer had been 

 added (25 per cent). 



After eight months of growth, the plants in all of the series except the 

 one to which sulfur had been added were heavily infected, were badly 

 stunted, and had produced no heads. Even the plants in the sulfur 

 series showed considerable infection, but those in three of the pots had 

 produced several heads. The sulfur apparently produced an acidity of the 

 soil which seemed to have delayed the attack of the fungus or lessened its 

 severity. 



From the literature and the preliminary test on the effect of fertilizers, 

 there appears to be a definite relation between the hydrogen-ion concen- 

 tration in the soil, and the severity of take-all. In order to further test 

 this point, the fungus was grown in culture on an acidity series consisting 

 of potato agars of nineteen different degrees of acidity ranging from pH 

 3.2 to 9.6, and on bacto-cornmeal agars of ten different degrees of acidity 

 ranging from pH 3 to 9.2. The degree of acidity of the media was deter- 

 mined by the colorimetric method as recommended by Clark. 10 



Cultures of Ophiobolus cariceti from three sources, in comparison with 

 one strain of Fusarium moniliforme Sheld., were grown on the media in 

 total darkness at room temperature (15° to 20° C). The average growth 

 of the three strains of Ophiobolus cariceti, and the growth of the single strain 

 of Fusarium moniliforme at the end of eight days, are shown in figure 4. 

 The results indicate that the take-all fungus requires a condition of alka- 

 linity for optimum growth, and may explain why additions of alkaline 

 substances to the soil have 1 been reported as favoring the fungus while 

 additions of acid-forming substances decrease the amount of infection. 



10 Clark, W. Mansfield. The determination of hydrogen ions, p. 1-317. 1920. 



