Nov. 1, 1919 Recent Studies on Sclerotium rolfsii Sacc. 135 



invade the entire tender stems (PI. 5, A), which soften considerably and 

 become covered with minute sclerotia. The fungus then works down- 

 ward and rots the mother sweet potato. With stored cabbage the rot 

 is confined to the two outermost layers of the head, which blacken and 

 turn soft (PI. 4, A). 



MANNER OF GROWTH 



The fungus was first studied by Halsted (d) and later by others, who, 

 however, did not give it a specific name. Saccardo (75) named it Sclero- 

 iiumroljsii from specimens sent to him by Stevens (17, p. 660-661). In pure 

 culture the growth of this organism is very distinct and can not easily be mis- 

 taken for any other species of Sclerotium fungus. Broadly speaking, this 

 organism is little influenced by the kind of artificial medium on which 

 it grows. Its myceleum is always white, fluffy, usually growing in strands 

 and in radial fans (PI. 4,B). This is especially true when an infected 

 fruit is placed in a bell jar in contact with the glass. In a very short 

 time the fungus grows out luxuriantly from the host on the surface of 

 the glass, on which it forms beautiful radial fans (PI. 6,B). The 

 sclerotia, in pure cultures, are very little influenced as to size by the nature 

 of the medium. In general they are of the size of a mustard seed (Pi. 4, B ; 

 3, A). This, in fact, agrees with the general description of other workers. 

 However, the sizeof the sclerotia is decidedly influenced by the kind of 

 host which the causal organism infects. For instance, on cantaloupes 

 and tomatoes the sclerotia are about the sizeof a mustard seed (P1.4,C). 

 However, on the orange the sclerotia assume such large proportions (PI. 

 3,B) as to resemble not those of Sclerotium roljsii but rather those of 

 Sclerotinia lihertinana Fck. However, the writer had no trouble to plant 

 these large sclerotia on artificial media and obtained again the normal 

 growth of Sclerotium rolfsii, with its accompanying mustard-seed-like 

 sclerotia. On the apple no sclerotia were formed at all. No experiments 

 have been made to determine the effect of fruit acids on the size of the 

 sclerotia of Sclerotium rolfsii, although it seems probable that the acid in 

 the orange is responsible for the abnormally large development of the 

 sclerotia. Peltier {11) has similarly observed that the sclerotia of 

 Sclerotium rolfsii on cultivated perennials in Illinois were much larger 

 in size than those found by the other workers. Similar observations 

 are recorded by Smith {16). This would seem to indicate that the kind 

 of host has an influence on the size of the sclerotia of this fungus. 



One further peculiarity which the writer observed in the growth of 

 the mycelium of this fungus is worthy of mention. Growth, instead of 

 proceeding indefinitely at the terminal end of the original mycelial thread, 

 comes to a standstill, a bud is developed near the tip end of the termi- 

 nal cell, and only the bud continues growth (fig. i, D-F). The hyphae 

 are seldom found growing singly but always appear in groups of several 

 branches (fig. i, G), which often anastomize and form regular strands. 



