Wire Stem of Cabbage 17 



inoculated when the oldest had been growing for twenty weeks. No 

 lesions were obtained on plants of that age, but very definite lesions were 

 produced on those eighteen weeks old and younger (Plate VII). It is 

 evident that the susceptibility gradually decreases with the age of the 

 plant. Many of the lesions on plants over twelve weeks old were not 

 typical for wire stem but were chiefly confined to a part of the stem only. 

 A growing period of twenty weeks in the field is practically long enough 

 to grow the early varieties to maturity. The variety used here, the late 

 "All Seasons," requires a longer time for maturing. 



Biologic specialization 

 Review of literature 



It is a matter of common knowledge that Corticium vagum is parasitic 

 on a wide range of host plants. The reader is referred to articles by 

 Duggar (1915) and Peltier (1916) for comprehensive reviews of the liter- 

 ature on this phase of the subject. 



Since the fungus is so widely distributed and occurs on such a great 

 number of hosts, the question of strains may well be considered. Occa- 

 sional reports of the discovery of definite strains emphasize the possibility 

 that important differences may exist within the species. Duggar and 

 Stewart (1901) early recognized the possibility of the existence of species 

 or strains of the fungus, and conducted cross-inoculation work. They 

 discontinued their experiments, however, before any definite conclusions 

 were reached. Shaw (1912) isolated Corticium vagum from peanuts, cow- 

 peas, jute, and cotton, and concluded from cross-inoculations that the 

 organism from jute is restricted to that particular host. Duggar (1915), 

 after a rather extensive study of the diseases caused by Corticium vagum, 

 came to the conclusion that, while many of the strains from different 

 hosts exhibit minor modifications, only that from rhubarb is of specific 

 importance. He mentions the occurrence of strains, the evidence of 

 which persisted for some time in the general appearance of the cultures. 

 He also gives a brief statement concerning the variation in size of sclerotia, 

 from the minute, scarcely visible ones, to those a centimeter or two in 

 diameter. 



In their publications in 1916, Duggar, Peltier, and Sherbakoff discussed 

 the possibility of specialization. Duggar concluded that the common 

 seedbed fungus in Germany and France is identical with the damping- 

 off fungus which has frequently been observed since the investigations 

 of Atkinson, and, further, that the damping-off fungus of this country is 

 Rhizoctonia solani Kuhn (Corticium vagum B. & C). Peltier conducted 

 extensive researches which included symptom studies; inoculation ex- 

 periments involving comparisons of forty-five strains of the fungus on 

 approximately 3000 cuttings, 2000 plants, and 7000 seedlings of various 

 sorts; observations on artificial media; measurements of mycelial cells; 



