i6o Journal of Agricultural Research voi. xix, no. 4 



In this case 6 per cent of the spikelets are blighted. This accords 

 with the percentage of primary lesions usually observed on seedlings in 

 the field. The sheaths below the panicles numbered 15, 32, and 35 

 were badly yellowed with halo lesions, 



(2) PRIMARY LESIONS ON THE FIRST LEAVES OF SEEDLINGS 



These primary lesions have been observed by the writer on more than 

 30 varieties of oats in Wisconsin in two different years. They may 

 appear as halos on any part of the leaf blade, but they more often occur 

 on the tips or margins of the leaves as shown by Plate 28. 



(3) EXPERIMENTS WITH TREATED AND UNTREATED SEED 



During the season of 191 7 two plots of oats were planted on soil which 

 had not previously been planted to oats. Untreated seed of each of 33 

 Wisconsin varieties was planted in April, and in May seed of the same 

 33 varieties was planted after having been soaked for 2% hours in i to 320 

 formalin (i pint to 40 gallons). Every one of the 33 varieties from 

 untreated seed showed halo-blight to at least some extent, the amount 

 decreasing as the hot weather came on. Wisconsin No. 14 showed the 

 heaviest blighting, and Wisconsin No. 25 was also heavily spotted. 

 Throughout the season not a single lesion was found on the 33 varieties 

 from treated seed. 



In April, 191 8, three parallel plots of oats were planted on soil not 

 previously planted to oats. Thirty-three Wisconsin varieties of 

 untreated 191 6 seed were planted in the first plot, 44 Wisconsin varieties 

 of untreated 191 7 seed were planted in the second plot, and 44 Wisconsin 

 varieties of treated 19 17 seed were planted in the third plot. Also 

 treated seed of Wisconsin No. 14 was planted as a fourth plot on the 

 experimental ground where oats were grown in 191 7. This seed was 

 treated by soaking for 3 hours previous to planting in i to 320 formalin. 



Counts of infections appearing in these plots were begun just as the 

 second leaf was coming out. On May 16, 17, and 18 primary lesions were 

 appearing on the first leaves of plots from untreated 191 6 and 191 7 seed, 

 the number of primary infections varying from less than i per cent to 8 

 per cent in each plot. These primary lesions on the 1916 plot would indi- 

 cate that the organism may live for two years on the seed. No lesions 

 were found at this time on the plot from 1917 treated seed. Counts were 

 made again in the untreated 191 7 plots on May 25, four or five days after 

 heavy driving rains, the normal incubation period for halo lesions. 

 Practically all the first leaves were found to be spotted, and lesions were 

 also appearing on the upper leaves. The condition in the 191 6 plot at 

 this time was about the same and continued to parallel that of the 191 7 

 plot. At this same time — 9 days after the first appearance of the disease 

 on the untreated plots — scattered halo spots and yellowed leaf tips were 

 beginning to appear on the treated plot, evidently by infection from the 



