454 
Journal of Agricultural Research 
Vol. XXIV, No. 6 
was isolated from 17 potatoes as compared with R. nigricans from 4, 
when R. nigricans was not included in the inoculum. On the other hand, 
R. artocarpi was obtained from only 6 potatoes as compared with R, 
nigricans from 11 (and in 3 of these cases the isolations were a mixture 
of R. artocarpi and R. nigricans) when R. nigricans formed a part of the 
inoculum. At 14° quite a different relationship was found. When R. 
nigricans was excluded from the inoculum, R. artocarpi was isolated from 
6 potatoes (4 of these isolations were a mixture of R. artocarpi and R. 
nigricans), R. nigricans from 29 and R. reflexus from 3. WTien R. 
nigricans was included in the inoculum, R. artocarpi was isolated once, 
a mixture of R. artocarpi and R. nigricans twice, and R, nigricans 33 
times. These results show, first, that the percentage of infection by R. 
artocarpi was higher when R. nigricans was excluded from the inoculum, 
although at 14° the difference was small; second, that 18° was more 
favorable for infection by R, artocarpi than 14°. This w^ especially 
evident when R. nigricans was excluded, in which case the infection by 
R, artocarpi greatly exceeded that of R, nigricans; third, that a tempera¬ 
ture of 14° was more favorable for R. reflexus than one of 18®; fourth, 
that R, artocarpi showed a slightly higher percentage of infection at 14^ 
than R. reflexus (these results correspond to those recorded in Tables V 
and VI); fifth, that R, tritici and R, oryzae at these temperatures infect 
less readily than either R. artocarpi or R. reflexus; and sixth, that R. 
nigricans infects more readily than any of the other species. This is 
shown, even when infection by R. nigricans is compared with that of R. 
artocarpi at 18°, because although R. artocarpi caused the greater part of 
the decay when R. nigricans was excluded from the inoculum, the reverse 
was true when i?. nigricans was included. This was true notwithstanding 
the fact that two cultures of R, artocarpi were used as compared with one 
of R. nigricans. Even assuming that spores of R. nigricans on the pota¬ 
toes were equal in number to the R. artocarpi spores in one culture and the 
number of spores in the cultures of the two were equal, the margin is much 
in favor of R. nigricans. It is believed that there is a greater number 
of spores in a culture of R. artocarpi than in a culture of R. nigricans. 
The percentage of infection by R. artocarpi and R. reflexus as compared 
with R. nigricans is not as high in these experiments as is shown in Tables 
V and VI at 14° C., but the concentration of the spores in the inoculum 
was not as high in the latter as in the former case. 
Tabi.]® VIII .—Organisms isolated from wounded sweet potatoes inoculated with a mixed 
suspension of spores of a number of species of Rhizopus 
Organisms employed. * 
Tempera¬ 
ture. 
Number 
of 
isolations. 
°C. 
Rhizopus tritici, 
oryzae, 
reflexus and 
18 
21 
artocarpi. 
14 
38 
Rhizopus tritici, 
oryzae, 
reflexus. 
18 
> 
17 
artocarpi and 
nigricans. 
1 
Organisms isolated. 
17 R. artocarpi. 
4 R. nigricans. 
' 2 R. artocarpi. 
4 R. artocarpi and nigricans, mixed. 
29 R. nigricans. 
^ 3 R. reflexus. 
3 R. artocarpi. 
3 R. artocarpi and nigricans, mixed. 
II R. nigricans. 
1 R. artocarpi. 
2 R. artocarpi and nigricans, mixed. 
33 R. nigricans. 
