44 
Journal of Agricultural Research 
Vol. XXIII, Mo I 
which signifies death of one plant only. The general succession of the 
various manifestations of the disease was essentially the same as in the 
first test and varied with the age of the plants. Thus, there were first 
some missing hills in those cases where the seed pieces were destroyed 
promptly in the ground, then damping-off symptoms showed on the 
young plants, and finally wilt, stemrot, and blight followed in older 
plants. As to the tuber production and tuber-rot, the following condi¬ 
tions were observed on the date of digging: 
EARLY PLANTING’ 
Lot (a): Only 9 hills produced tubers, of small size; a severe rot in 3 hills 
Lot (b): Every hill produced tubers, all undersized; severe rot in 4 hills. 
LATER PLANTING 
Lot (c): Only 5 hills produced tubers, undersized; severe rot in 1 hill. 
Lot (d): Tubers in every hill, varying in size; severe rot in 4 hills. 
It appears from the foregoing data that the most serious infection with 
Sclerotium No. 126 took place in the later planting or later in the season 
in the earlier planting and, quite the contrary, with Sclerotium No. 127 
the most serious infection took place in the earlier planting and very' 
little infection was observed in the later planting. These results indicate, 
therefore, that the Arkansas strain of the fungus is more adapted to 
cooler temperatures, while the North Carolina strain is more adapted to 
warmer temperatures. 
The total number of hills which became infected with culture No. 126 
in both plantings in this experiment was 19, and the total number of 
hills which became partially or wholly infected with culture No. 127 in 
both plantings was only 8. This apparently weaker pathogenicity of 
the latter strain is quite in accord with the results obtained during the 
preceding season. 
EXISTENCE OF STRAINS OF SCLEROTIUM ROLFSII 
The markedly different parasitic activities of the two Sclerotium cul¬ 
tures and their different behavior in the field at different time of the 
season obviously suggest the existence of strains in Sclerotium rolfsii. 
Taubenhaus 4 summarizing the results of his recent w r ork, stated that— 
There are no varietal nor physiological strains in Sclerotium rolfsii . 
It is self-evident, however, that this assertion may be regarded as cor¬ 
rect with reference only to those strains which were included in his 
studies and that the generalization of the characteristics of these strains 
is not at all warranted. As it is seen from the foregoing account of the 
writers’ experiments, their two strains reveal a decided physiological 
difference. Furthermore, these two strains exhibit a distinct morpho¬ 
logical difference, namely, in the size of the sclerotia, as shown in Plate 3, 
A to C. The individual sclerotia vary in size within the strain, and their 
average size may be larger or smaller, depending on the kind of medium 
and environmental conditions; but when considered relatively, on the 
same medium, at the same age, grown under the same environment," the 
sclerotia of the culture No. 126 are always larger than the sclerotia of the 
culture No. 127. Besides, there is a peculiar tendency in the strain 
No. 126 when food supply is abundant to mass up the sclerotia in large 
clusters (PI. 3, C) which has not been noted in the < ‘microsc!erotial ,, 
strain No. 127. The sclerotia in the clusters are often of a much larger 
diameter than the individual sclerotia and tend to become elongated, 
* Taubeniiaus, J. J. Or. err. 
