340 Journal of Agricultural Research voi. xv, no.6 



over 48 hours, this decoction together with the mycelium, which often 

 formed a pellicle, was poured into a well in the potato made as described 

 above and sealed over with a cover slip set in vaseline. 



The inoculated potatoes were then put into moist chambers with wet 

 filter paper in the bottom. Inoculations by this method were usually 

 successful, except for organisms that have been classed as strictly sapro- 

 phytes. By this method sufficient moisture and nutrient substances 

 were supplied to give the fungus a start. The method was later modified 

 somewhat to facilitate manipulation. Instead of covering the well with 

 a cover slip, the hole was plugged with cotton. If tightly plugged, 

 enough of the decoction was retained to serve the desired purpose even 

 though the specimen was turned with the well to one side or downward. 

 Coupled with the proper temperature conditions, such extreme methods 

 usually gave positive results with organisms that otherwise consistently 

 gave negative ones. It may be argued that where such extreme measures 

 are required the organism should not be classed as a rot producer. The 

 only answer to this is that in our hands they are rot producers under 

 artificial conditions only when subjected to this test and most of the 

 organisms studied require such a method. This applies to some of the 

 most common forms consistently isolated from a rot of a definite type, 

 and of which there can be little question of their causal relation. 



SOFTROT AND RINGROT 



There are two storage-rots of sweet potatoes caused by Rhizopus nigri- 

 cans Ehrbg. : Softrot and ringrot. The former has long been known as 

 the softrot of sweet potatoes in storage. Halsted {12), who, we believe, 

 was the first to recognize it as such carefully described it in 1890. In 

 1892 a rot of quince (jj) was attributed by him to the same fungus. 

 Since that time there have been other observations and experiments 

 whiclfcshow that R. nigricans is responsible for rots of fruits and vegetables 

 under suitable conditions. Behrens (5, p. 515-516), Wormald (41), and 

 Hanzawa {16) have all found it causing a rot of tomatoes. In 1908 

 Morse {28) attributes a rot of fruit to it, and Orton (29) a year 

 later found the same fungus associated with the "leak" of Irish potatoes 

 in the San Joaquin Valley of California. Edgerton {10) attributes a 

 heavy loss of figs to the same fungus. In 191 6 Stevens and Peterson 

 {32), in a study of strawberry fungi, mention R. nigricans as the cause 

 of considerable loss to the berries at their destination. A more extensive 

 study of this same trouble was later made by Stevens and Wilcox (jj), 

 who conclusively proved the parasitic nature of the fungus and studied 

 the factors which contribute to its destructiveness. While this brief 

 survey of the literature shows R. nigricans to be a relatively common 

 rot-producing organism of various hosts, it is best known as the cause 

 of softrot of the sweet potato, to which it probably causes more monetary 

 loss than to all the other crops combined. Compared with other organ- 



