Journal of Agricultural Research 
Vol. IX, No. 22 
414 
SOURCE OF MATERIAL 
The cultures of R. solani on which the following studies are based were 
obtained from stems and tubers of potatoes grown in Florida and 
northern Maine. The isolations were made during the summers of 1915 
and 1916, so that the comparisons are made with cultures of compara¬ 
tively the same age. For the sake of convenience they are here desig¬ 
nated ‘ ‘Ri,” 1 *R2,” 1 ‘R3,” etc. Ri, R2, and R3 were isolated in Maine 
during the summer of 1916 from # the base of affected plants. R4, R5, 
and R6 were obtained from the same locality from the inside of potato 
stems. R7 was isolated from tubers obtained at Hastings, Fla., in 1915, 
and R8 from tubers in Maine during the summer of 1915. Throughout 
these studies all the strains, from Ri to R8, could not be distinguished, 
with the single exception of R5. In presenting the results, therefore, 
R5 will be compared with a representative of one of the other cultures. 
The cultures from the stems were obtained from plants showing a girdling 
and hollowing at or near the surface of the ground (PI. 25, A), This con¬ 
dition appeared to be a secondary stage in a malnutrition trouble briefly 
described by Edson and Schreiner. 1 
distinguishing characters 
The points of difference between R5 and the other strains, as here pre¬ 
sented, can be grouped as pathological, as shown by inoculation experi¬ 
ments; physiological, as shown by the reactions on different media; and 
morphological, as shown by the measurements of mycelium, of surface 
sclerotial cells, and of diameters of germ tubes produced by germinating 
sclerotial cells. 
PATHOLOGICAL CHARACTERS 
Inoculations were made in the field on healthy growing plants. The 
method of procedure was to wash any dirt from the stems, make a 
slight incision with a flamed scalpel, and insert a bit of a young growing 
culture into the wound. The control plants were likewise injured. A 
number of such inoculations with R5, Ri, R2, R3, etc., and a number of 
undetermined fungi also isolated from diseased stems, resulted in the 
production of very pronounced lesions with R5. The lesions produced 
by Ri, R2, etc., were indefinite, as was also the case with all the unde¬ 
termined fungi. The injured control plants remained healthy. Plate 
25, B t illustrates the results of one of the series of inoculations. The three 
stems to the left were inoculated with R5, the next two with Ri and R2, 
and the last shows the condition of the control. 
Inoculations were also repeated in the greenhouse, with results practi¬ 
cally similar to those described above. 
1 Edson, H. A., and Schreiner, Oswald. A malnutrition disease of the Irish potato ^ its control, In 
Phytopathology, v. 7, no. x, p. 70-71. 19x7. 
