NOTES ON THE MORPHOLOGY AND SYSTEMATIC RELA- 

 TIONSHIP OF SCLEROTIUM EOLFSII SACC* 



By B. B. Higgins 

 Plate 29 



In spite of the proved parasitism and general occurrence of Scle- 

 rotium rolfsii in the warmer portions of the United States, very little 

 is known in regard to the structure cf the mycelium and of the scle- 

 rotia of the fungus. The few data that have been published on the 

 subject have contained so many errors as to be confusing rather than 

 clarifying. It, therefore, seems desirable to pul^lish, at this time, a 

 few notes that may be helpful to others who come into contact with 

 this fungus. 



The reputed appearance and disappearence of the fungus in fields, 

 and its other peculiarities, have led to investigations with the hope that 

 some fruiting stage would be discovered. So far no spores have been 

 found ; but certain characteristics of the mycelium have been noted, 

 which are of considerable help in distinguishing the mycelium of this 

 fungus from that of several others that attack plants in a somewhat 

 similar manner. These characters also suggest, in a general way, the 

 spore forms that one should expect to find associated with this myce- 

 lium. 



On fleshy plants and on fruits, such as cantaloupe, where food and 

 moisture are abundantly available, the growth of S. rolfsii is very 

 vigorous and characteristic. The mycelium usually forms broad white 

 sheets and a profusion of sclerotia develops ; but on small or more 

 woody stems, such as those of sweet potato slips or of pepper plants, 

 the growth is often very scanty and impossible to distinguish macro- 

 scopically from any one of several other fungi that may attack these 

 plants. Even when such plants are placed in a moist chamber, scle- 

 rotia often fail to develop. 



MYCELIUM 



The mycelium is rather coarse, with large cells (2-9 x 150-250/*). 

 The feeding branches which enter the medium or the host tissue 

 and those which enter into the formation of the sclerotia are of the 

 more slender type (about 2/x, in diameter). In the broader threads 

 clamp connections occur characteristically, two at each division (figs. 



Pjiper nunibpr 15, Journal Series, Georffiu AKricultural Experiment Station. 



[167] 



