448 
Journal of Agricultural Research 
Vol. XXIV, No. 6 
held for a few weeks below this temperature they almost invariably 
decayed with Mucor racemosus Fres. There is nearly always loo per 
ceint infection by M. racemosus under cold storage conditions and also in 
the infection chambers below 6°. 
Tabl^ III .—Isolations from wounded sweet potatoes inoculated with R. tritici and R, 
nigricans and held at different temperatures 
1 P.= Penicillitim; bact.—bacteria; R. n.—R]iizopus nigricans; R. t.— Rhizopus tritici; and M= Mucor. 
If this method of wounding is employed, whether the potatoes are 
inoculated or not, the percentage of infection by R. tritici and R. nigricans 
is nearly always loq at temperatiures above 30° and below 20° C., respect¬ 
ively, the percentage being lower between these temperatures. 
Sweet potatoes are sometimes injured by heat at 40° C. if the humidity 
is high, and badly injured at 44°, the highest temperature at which 
R, tritici caused infection. 
TYP^ THR^^ 
The third type of experiments was designed to determine how 
effectively other species compete with R, nigricans in producing infection 
at the usual storage temperatures. The potatoes were wounded as in pre¬ 
vious experiments, some having been previously washed in tap water to 
reduce if possible the number of spores present on their surfaces and 
