Wire Stem of Cabbage 15 



Finely chopped stems of diseased seedlings were next thoroughly mixed 

 into virgin soil, and untreated seed was sown. Virgin soil not containing 

 the diseased stems, and soil in which diseased plants had been growing, 

 were used for comparison. The seed in the first flat germinated poorly. 

 Most of the plants were killed outright, and the remainder developed 

 wire stem. The seed in the fungus-infected greenhouse soil gave normal 

 germination and considerable damping-off, followed by the wire-stem 

 stage. The seed in the clean soil produced no diseased plants. This 

 experiment indicates that parts of diseased plants may harbor the patho- 

 gene, that the fungus is not carried in the seed, and that the amount of 

 inoculum in the soil is a factor in determining whether the plants will be 

 killed outright or will develop wire stem only. 



Diseased stems were next examined, and the typical, broad, hyaline 

 mycelium of Corticium vagum was demonstrated in the outer tissues of the 

 plant. Hundreds of tissue plantings from diseased stems were made on 

 potato agar, and the fungus was consistently isolated throughout the 

 summer. 



In the winter of 1921, soil-infection experiments with pure cultures of 

 the fungus were conducted, and the results obtained were conclusive in 

 establishing the pathogenicity of the fungus. In addition, these ex- 

 periments developed the most satisfactory method of inoculation. This 

 method consisted in growing the fungus on sterilized wheat in wide-mouthed 

 bottles, adding a kernel of this substrate to the base of the seedling, 

 and covering slightly with soil. This procedure was followed exclusively 

 in all of the later experiments unless otherwise stated. In the early 

 experiments the inoculum was added to the soil directly, but this method 

 was not satisfactory for wire-stem investigations as the number of plants 

 pushing through the surface of the soil was greatly decreased. 



In these early experiments the inoculum was added to thirty-six 4-inch 

 pots of sterilized soil as follows: growing on potato agar, six pots; growing 

 on wheat, fifteen pots; growing on soil-cornmeal mixture, fifteen pots. 

 Six pots were maintained as controls. Twelve treated seeds per pot 

 were sown immediately after the inoculum was added to the soil. In 

 the infected soil, germination and growth were very poor. In the controls, 

 all of the seed germinated and the plants remained healthy. The check 

 plants were inoculated later by adding the inoculum to the base of the 

 stems, and all of them developed the disease. Isolations were made, and 

 Corticium vagum and a species of Fusarium were obtained. In later 

 inoculations only the former fungus produced the disease. Many such 

 inoculations and reisolations in the past two years have removed all 

 possibilities of doubt concerning the pathogenicity of this particular 

 strain. 



