8 Levi Otto < Iratz 



were also thai the cells of these two strains were different in shape, but 

 the extreme variation in any one of the strains makes it impossible to 

 state with certainty that this was uniformly the case. Daily microscopical 

 examination of the cultures (potato agar) up to the seventh day revealed 

 the fact that the sclerotial-cell formation was considerably slower in the 

 strain from aster, and still slower in the strains from bamboo and cabbage, 

 than in any of the strains from potatoes. In the strains from potatoes 

 the rate of this formation was about uniform. 



The fruiting stage 



Two forms of hyphal growth similar to those described by Rolfs (1904) 

 were frequently associated with wire stem. The light, hyaline form was 

 usually found within the cortical tissue of the plant attacked. Fre- 

 quently the dark form was found growing about the base of the seedling. 

 With the potato strains, on potatoes, this was especially noticeable. In 

 the inoculation experiments on potatoes, a large proportion of the stems 

 were covered with this dark, weblike mycelium. An unsuccessful attempt 

 was made to bring this mycelium into fruiting by placing the plants under 

 bell glasses. With the cabbage strain, on crucifers, this mycelium was 

 also very prevalent. The typical, white, granular, fruiting layer appeared 

 frequently on the small stems of the cabbage, turnip, and radish seedlings, 

 but it was only in one case, on turnips, that the basidia, with the sterig- 

 mata and the spores, were actually demonstrated. Several basidia, but 

 only two spores, were observed. This limited number of fruiting structures 

 is not regarded as sufficient to identify the organism, but from the measure- 

 ments and general appearance they were considered identical with those 

 described by Rolfs for the perfect stage of Corticium vagum. At no time 

 in the numerous inoculations made was this " fruiting " mycelium from 

 the potato strains observed on the cabbage seedlings, or that of the cabbage 

 strain on the potato stems. 



The temperature range for growth 



Accurately controlled temperature chambers were available for only 

 the higher temperatures. A fair idea concerning the minimum temperature 

 for growth was obtained by placing petri-dish cultures in the bottom of a 

 refrigerator where the temperature limits were about 9° to 11° C. Other 

 cultures were placed in about the center of the refrigerator, where the 

 temperature limits were approximately three degrees higher, and still 

 others at the top, where the fluctuation was somewhere between 14° and 

 16° C. Another set of petri-dish cultures was held at room temperature, 

 and others in controlled temperature chambers. The minimum and maxi- 

 mum temperatures for growth were found to be approximately 9° and 

 31° C. The optimum is not sharply defined, but is somewhere between 



