PATHOGENICITY OF H. SATIVUM 27 



the host tissue occurred so rapidly that further development of the 

 fungus was checked. 



While no control experiments were made with soil or leaf infection 

 on growing plants, results obtained in the greenhouse agreed in general 

 with those obtained on the temperature relations of the fungus. When 

 the average temperature was between 75 and 85 F., much better infec- 

 tion was obtained than when the average was lower. Better results 

 were obtained on an inner bench over the steam pipes than on an outer 

 bench next the outside wall on the west end of the house where it 

 was always cool, and vigorous plants developed in spite of heavy Foil 

 inoculation. 



These results also agree with those reported by McKinney (8). 

 He says, "Controlled soil temperature experiments, conducted in the 

 'Wisconsin temperature tanks,' and field experiments show that seedling 

 infection hi both spring and winter wheat and in spring barley is great- 

 est at relatively high temperatures. The optimum temperature appar- 

 ently lies between 26 and 28 C. This is very near the optimum rate 

 of growth of H. satiznim in pure culture." 



INFLUENCE OF TYPE OF SOIL 



The statement has already been made that particularly severe infec- 

 tions of Helminthosponuni foot- and root-rots were observed during 

 the summer of 1920 on sandy soils and on peat soils in certain localities 

 in Minnesota. Consequently one of the first tests undertaken was a 

 study of the development of the disease in different types of inoculated 

 soil in order to gain, if possible, an insight into the individual factors 

 which might be influencing the situation. 



A heavy loam, a sandy loam, a sand, and a peat soil were selected 

 for use. The heavy loam was a black dirt used without modification ; 

 the sandy loam was obtained by mixing two parts of the heavy loam 

 with one- part of quartz sand; and the sandy soil by mixing one part 

 of the heavy loam with two parts of coarse sand. All this soil was 

 passed through a 5-millimeter mesh screen before being packed into 

 the pots. The peat was a high-lime peat obtained from Anoka County 

 through the Division of Soils, and fertilized according to directions 

 with acid phosphate and potassium chloride to secure maximum yield 

 from this particular type of soil (i). 



Small pots of steam-sterilized soil were planted with Marquis wheat 

 and Lion barley. After the seeds were planted, the soil was watered 

 several times with a heavy suspension of Helminthosporium spores. 



