294 Journal of Agricultural Research voi. xvi, No. n 



LATE OHIO DISEASED SEED (TABLE I, H-l) 



In the fall of 191 5 several fields were visited for the purpose of staking 

 diseased hills of potatoes. The hills selected all showed blackening of 

 the stems and death of the tops, with many cases of rot in the tubers. 

 At harvest the badly decayed tubers were discarded for the reason that 

 they were in no condition to keep through the winter. The tubers 

 showed a large percentage of vascular discoloration, and the remainder 

 were believed to be infected, though not seriously. All came from hills 

 affected by Fusarium-bUght. Cultures were made from the stem end of 

 all showing discoloration, and all yielded species of Fusarium. The 

 tubers were cut and planted as twins in adjacent rows and given the same 

 culture as the lots mentioned above. Table I, H, shows the performance 

 of such seed of the variety Late Ohio in the year 191 6. 



The complete absence of any plants falling in the D columns is the 

 outstanding feature of this table. At best, only the 6 pairs represented 

 in DHDH square could be said to show the results of vascular infection, 

 especially from the occurrence of 5 of them in the DHDH square in Table 

 I, I. Compared with Table I, E, which represents a healthy Early Ohio 

 variety, the advantage in health is with the home-grown seed. 



A table representing the places in which the 50 tubers (56.66 + per 

 cent) showing decided vascular discoloration fell, is shown by Tablel.I. 



PEARL DISEASED SEED (TABLE I, J-k) 



One lot of diseased seed consisting of 138 tubers. Pearl variety, acquired 

 in the same manner as the Late Ohios, were cultured from the stem-end, 

 and planted under the same conditions as other lots. Table I, J illus- 

 trated the performance of this badly diseased seed stock. 



Two things are conspicuous here : The lack of plants in the D columns 

 (one in DO) , and the comparatively large number in the O and the HD 

 columns. These are not to be accounted for here altogether because of 

 their vascular discoloration, because Table I, K, which represents where 

 the 53 tubers (38.41 — per cent) fell which showed discoloration, does not 

 account for the majority. Plainly these plants have been weakened by 

 disease, their power of resistance lessened, and their vigor impaired. 

 Examination showed that soil infection acted here to produce the disease, 

 but a comparison of Table 1, J, with Table \, A, reveals the great weak- 

 ness acquired by these plants, which made them so easily attacked. 

 These tubers were extreme cases, being stock that would not ordinarily 

 get into commercial seed. The circumstances surrounding this lot of 

 of seed tends to explain the true reason why farmers of the Greeley Dis- 

 trict prefer to plant newly introduced seed every two years. 



Table I, K, represents the places in which that seed fell which showed 

 pronounced vascular discoloration, according to the place they occupy 

 in Table L J- 



