14 Levi Otto Gratz 



noted. Twenty days after the cultures had been transferred, the petri 

 dishes at the intermediate temperatures were practically covered with 

 sclerotia. Only a few had appeared at the second and third lowest tem- 

 peratures, and none at the lowest and the three highest temperatures. 



Pathogenicity 

 Historical aspects 



According to Duggar (1915), Eidam (1888) was probably the first to 

 mention the ability of Corticium vagum to cause a seedling disease of small 

 plants. The host mentioned was the beet {Beta vulgaris L.). No complete 

 account was given to prove that this fungus was the causal organism. 

 Atkinson (1895), by his careful description of the general characteristics 

 of the mycelium, and by his observations on the " sclerotoid bodies " 

 produced by his " sterile fungus," leaves no question as to the identity 

 of the organism. He, however, did no culture work to demonstrate its 

 pathogenicity. Duggar (1899) attributes the damping-off of the sugar 

 beet in New York to this fungus. Fawcett (1909), basing his conclusions 

 on the identification of the fungus by Orton, who declares it the same 

 organism as that on potatoes, attributes the damping-off disease of cabbage 

 to Corticium vagum because of its constant association with the host. 

 Sherbakoff (1916) is apparently the only worker who has made any inocula- 

 tions of cabbage or other cruciferous seedlings to demonstrate that Corti- 

 cium vagum is capable of producing the disease in question. 



Experimental data 



The writer first observed wire stem in April, 1920, on plants which were 

 being transplanted into the field. Very few of these plants had been 

 killed by the fungus, but a large amount of wire stem was found. In 

 order to determine the source of the inoculum for infection under natural 

 conditions, seeds previously disinfected with a 1-1000 mercuric-chloride 

 solution for twelve minutes were planted in flats in (a) virgin soil from 

 woods, (b) untreated soil from the greenhouse in which diseased plants 

 had been grown, (c) soil from the greenhouse in which diseased plants 

 had been grown and treated with either steam or formaldehyde. Several 

 hundred plants were grown in each of these different soils. All of the 

 plants in the virgin soil remained healthy, while all of those in the un- 

 treated greenhouse soil showed wire stem. Only a few plants in the 

 treated greenhouse soil were affected. These results indicated that the 

 soil carried the inoculum. Germination was greatly reduced in the in- 

 fected soil, and an examination of the seed showed that many of the sprouts 

 had emerged a millimeter or so and were then killed. Damping-off was 

 noticed first. Within approximately ten days the plants that had not 

 been killed outright developed wire stem. Later experiments confirmed 

 these indications that the inoculum was harbored in the soil. 



