PATHOGENICITY OF H. SATIVUM 29 



same in the heavy loam and in the sand. This would indicate that these 

 two types of soil had practically an equal influence on the development 

 of the disease. 



The difference was less pronounced in the sandy loam, showing that 

 here the disease had least influence on the size of the plants. The great- 

 est difference in height was in the peat soil, indicating that here the 

 disease had most influence on the growth of the plant. From these 

 results it is apparent that root-rot of barley produced the greatest effect 

 on the host in the peat, a less marked effect in the sand and heavy loam, 

 and the least effect in the sandy loam. On the whole, the differences 

 were very small. The further development of the disease on the barley 

 plants was not followed. 



The conclusions to be drawn from the height of the wheat plants at 

 this stage must be derived from comparisons between the differences in 

 the height of diseased and check plants in the same type of soil. It is 

 obvious that the effect of the disease is much more marked on the wheat 

 than on the barley. The least effect of the disease on the growth of the 

 plants was obtained in the heavy loam. There was practically an equal 

 increase in effect in the other three types of soil. 



The wheat was then transplanted to larger pots of inoculated soil. 

 In each case, the most severely diseased plants were transferred. After 

 transplanting, the check plants grew much faster than the diseased 

 plants, and headed several days earlier. Plate III shows the compara- 

 tive vigor and size of the plants in the different types of soil at maturity. 

 Final observations were made on the Marquis wheat just before the 

 heads began to turn yellow. The plants were removed from the soil, 

 carefully washed, and examined for foot- and root-rot. 



In the heavy loam soil, both diseased and check plants averaged 

 3.5 culms per plant. While the severity of infection, measured by the 

 degree of browning at the base of the plant, was moderate, there was 

 very little difference in the extent of the root systems. The check 

 plants headed four days earlier than the diseased plants and were con- 

 siderably more vigorous. A slight browning occurred at the base of 

 most of the mature check plants which resembled slightly a light infec- 

 tion by Helminthosporium. The lesions, however, were less definite 

 and no organism was obtained from tissue cultures. H. sativnm was 

 isolated from the base of diseased plants. 



In the sandy loam, the average number of culms on each diseased 

 plant was 3, on each check plant 2.5. The basal infection was moderate. 

 There was little difference in the root systems. 



In sand the average number of culms on each diseased plant was 3, 

 on each check plant 2. The infection at the base of the diseased plants 



