282 Journal of Agricultural Research voi. xvi. No. ix 



watered with sterile water. The flats were set on the edge of a field, 

 where ordinary weather factors would act as normally as possible. These 

 flats were noted finally on September 8, 191 7. The control plants were 

 healthly throughout, with normal foliage and stems 10 inches long. In 

 the first flat only one tuber of the inoculated seed sent up a pair of sprouts. 

 One of these was dead and the stem blackened for 2 inches above the 

 ground. Although the seed piece was thoroughly decayed, the other 

 sprout appeared healthy, as shown in Plate 37, B, It is characteristic 

 in every respect of the field blight. A closer view of the seed piece, 

 together with a control seed piece from the same flat, is shown in Plate 

 37, C. In the second flat two seed pieces failed to germinate, owing to 

 decay. One was dead, and the stem was blackened. In the third flat 

 one seed piece failed to germinate, while four sent up sprouts. These 

 had all wilted thoroughly, though death had not yet occurred. None of 

 these plants had been subject to frost. Isolation cultures were made 

 from all the diseased plants from the three flats, and F. oxysporum was 

 recovered in pure culture in each case. 



On September 9, 1917, three flats were prepared for inoculation. 

 Sterile soil was used. Seed pieces of the Pearl variety were inoculated 

 with a spore suspension of F. oxyspor^im in the usual way. The spore 

 suspension was made from cultures taken from the diseased seed pieces 

 of the inoculation experiment of July 17. No controls were made, 

 because of lack of space. Owing to the lateness of the season, these 

 flats were taken to Fort Collins, Colo., where, through the courtesy of the 

 Horticultural Department of the Agricultural College, they were placed 

 in the greenhouse. The plants were not seen until November 3; at 

 which time all were dead with the exception of three plants, then about 

 to die. 



On August 13, 1 91 7, nineteen whole tubers which had been planted in 

 the field for three weeks and which had sent up sprouts were inoculated. 

 Fourteen of them were inoculated with a spore suspension of F. oxysporum 

 poured into glass tubes entering the epidermis of the tuber; five were 

 treated with sterile water as controls. In each case the plant had a 

 healthy, vigorous start. On September 9 the plants were taken up and 

 examined. The seed pieces of the controls were sound and the plants 

 healthy; seven inoculated plants were healthy, though the seed piece 

 was decayed; the other seven were wilted, the stem was blackened, and 

 the seed piece was thoroughly decayed. 



On August 10, 1 91 8, sixty-one plants planted in sterile soil in flats were 

 inoculated with F. oxysporum. Sixteen plants in flats in sterile soil were 

 treated as controls. The method of handling was different from that 

 used before. The seed pieces had been planted with the cut surface 

 turned up, about a month previously, and the flats left in a cool place. 

 They were watered periodically with sterilized water. By August 10 the 



