480 



FUNGOUS DISEASES OF PLANTS 



appeared. An examination of the plant after death shows that all 

 of the smaller roots have been killed, and these readily break off 

 as the plant is pulled from the soil. At this time the main root 

 as well as the fibrous root system is infested with a weft, or with 

 strands,, of the dirty yellow or buff-colored fungus. 



The mycelium penetrates the bark and also the wood of the 

 roots. It does not, however, extend into the wood far above the 



surface of the soil. This 

 organism in the United 

 States was first studied by 

 Pammel and provisionally 

 referred by him to the ster- 

 ile form Ozonium aurico- 

 mum Lk. He seems to 

 have had doubt of the cor- 

 rectness of this reference 

 from the beginning, and 

 Shear now regards this 

 American fungus as one 

 clearly distinct from 

 Link's species, and he has 

 accordingly given it a new 

 specific name, as above. 



This fungus may be 

 grown on cooked potato 

 and other nutrient media, 

 but the organism is none 

 too readily isolated. No 

 spore stage has been found 

 in culture, nor definitely 

 associated with it in the 

 open. A careful study of 

 the organism in the field has given indications, however, that an 

 oidium stage may be developed under certain conditions, and that 

 the organism is probably a Basidiomycete. 



It seems that no successful inoculation experiments have been 

 reported with this fungus. During two seasons I attempted to 

 transfer the disease to potted cotton p^nts in the greenhouse. 



FIG. 240. OZONIUM OMNIVORUM ON ROOTS 

 OF COTTON 



