Wire Stem of Cabbage 23 



Two strains from potatoes (indicated by daggers in table 8) produced 

 definite dark brown wefts of mycelium on the stems of the plants. Some 

 of the pots were placed in a moist chamber, and some under bell glasses, 

 with the hope that the perfect stage might be obtained, but these efforts 

 were unsuccessful. It is to be noted (table 8) that these two strains pro- 

 duced definite lesions on either the stem or the roots, and also producetl 

 the most and the largest sclerotia on both the old seed pieces and the new 

 tubers. It is worthy of note that of these two strains, the one producing 

 the most lesions and sclerotia was the one which was isolated from the 

 potatoes from Canada two years earlier and at that time demonstrated 

 to be non-pathogenic on cabbage (page 19). Here, then, it is to be observed 

 that the pathogenic cabbage strains produce neither lesions nor sclerotia 

 on any part of the potato, but it is possible to get infection with them on 

 cabbage under a wide range of conditions; also, that the strains from po- 

 tatoes, non-pathogenic on cabbage, produce definite lesions and sclerotia 

 in numbers on their own host. 



Extensive inoculation experiments were next undertaken with freshly 

 isolated potato strains to determine conclusively whether the differences 

 in pathogenicity of the various strains were due to a specific relationship 

 between host and parasite, or to other factors. From forty to fifty seeds 

 of cabbage were sown in sterile soil in 4-inch pots. When the seedlings 

 were two inches high, inoculations were made with forty-one freshly iso- 

 lated strains from potatoes. Thirty-nine of these were obtained from 

 sclerotia from five different lots of tubers from three different counties in 

 New York, and two from different lots of southern potatoes bought at a 

 retail store. Two pots were used for each strain. This experiment was 

 repeated later in duplicate, as before, with twenty-two of the strains. 

 Ten pots were reserved as checks in both trials. Eveiy seedling was ob- 

 served, and eight slightly discolored stems were found in the first trial. 

 This, however, was a discoloration only and not a case of wire stem or 

 damping-off. In the second trial, all of the seedlings in one pot damped- 

 off, as did also five others in each of two other pots. This damping-off 

 was evidently a result of improper sterilization of the soil, since no dis- 

 eased plants were produced in any of the duplicates in the above series, 

 and since twelve pots of seedlings had to be discarded before the inocula- 

 tions were made. The seedlings in five of the controls developed the 

 disease later. The plants in four pots in each of these trials were inocu- 

 lated with the cabbage strain, and practically 100 per cent of infection 

 resulted in every case. All of the checks remained healthy except where 

 the soil was not properly sterilized. From these data, where from 35 to 

 50 seedlings were inoculated in each of 125 pots, or ;i total of from 4500 

 to 5000, witli negative results, the conclusion is warranted that the freshly 

 isolated potato strains are not pathogenic on cabbage. 



Parallel with the preceding experiment, a strain of Corticium vagum 

 isolated from asters in December, 1922, at the college greenhouse, 



