PATHOGENICITY OF H. SATIVUM 37 



Final data were taken just before the heads ripened. An attempt 

 was made to obtain a quantitative estimate of the percentage of plants 

 infected for the whole plot and an average of the degree of infection 

 on the roots, foot, and node from individual plants. For this purpose, 

 approximately equally large groups of plants were dug from the center, 

 and also from each corner of the plots, two feet from the margins. 

 Ten plants were taken from each group and for these fifty plants, the 

 following data were recorded : the number of culms which headed ; the 

 number of tillers which did not head ; the degree of infection indicated 

 as heavy, moderate, or light on the roots, foot, and nodes. Finally, the 

 seed from each plot was weighed after threshing and the yield per acre 

 was calculated from this. These data are summarized in Table XI. 

 In order to obtain a simple mathematical expression for making com- 

 parisons, the percentage of heavy infections was multiplied by 10, the 

 moderate by 5, and the light by i, and the sum was taken as the index 

 of the total infection. In order more easily to make comparisons, these 

 sums were reduced to unity. Finally, these expressions for root and 

 foot infections were totaled to obtain a means of comparing the com- 

 bined foot- and root-rot with the relative amount of soil moisture and 

 with the yield. For the sake of comparison these were also reduced to 

 unity. In some cases the Helminthosporium infections were so com- 

 plicated by Fusarinin infections that it is quite impossible to say how 

 much of the damage was due to each organism. This was especially 

 true on the Manchuria barley. In general, the amount of injury was 

 small. Altho the root-rot and the basal infection as measured by the 

 degree of browning was sometimes heavy on a large number of plants, 

 the plants were not noticeably stunted or immature as is often the case 

 in severe cases of foot-rot. On the whole, there was more foot- and 

 root-rot on the barley than on the wheat. The Lion barley alone shows 

 an increase in the amount of foot-rot as the relative amount of soil 

 moisture is increased. The differences are so small, however, that they 

 can not have much significance. There were no indications of a correla- 

 tion in yield with either the relative amount of soil moisture or the 

 amount of foot- and root-rot. For both varieties of wheat, foot- and 

 root-rot was slightly worse on the driest plot. In no case did the rela- 

 tive amount of soil moisture or infection influence the tillering of the 

 plants. 



