Jan. ig p 1917 
Blackleg Disease of Potato 
107 
The organism received from Appel as B. phytophthorus produced no 
apparent growth upon potato cylinders, but the liquid below was clouded, 
and the substratum grayed or slightly browned. 
The organism received from Schuster as B. phytophthorus upon cooked 
potato agreed with the detailed description of the group given above, 
except that in the earlier stages the growth was more abundant, and at 
all times it had a distinct yellow color, especially on the more moist por¬ 
tions of the slant. This agreed quite closely with the “honey-yellow'' 
color which Appel originally described for B. phytophthorus . The medium 
was considerably grayed and had a brownish tinge. 
Gelatin stabs. —The behavior of the various named species with 
reference to liquefaction in gelatin stab cultures had been used also as a 
differential character. While all are reported as liquefiers, Harrison (17), 
who did a large amount of work with B. solanisaprus , reports this organ¬ 
ism as very slow in this respect, liquefaction not beginning until 35 days, 
and not complete in 44 days. The others are reported to liquefy gelatin 
much more rapidly, although van Hall (15) stated that with B. atrosep- 
ticus liquefaction was variable. 
Therefore in the present studies particular attention was paid to the 
behavior of the various organisms in gelatin stabs. With regard to B. 
atrosepticus , B, solanisaprus , B. melanogenes, IIIA, SE, and IIP, the 
behavior was somewhat erratic on this medium, especially when the 
“gold label” gelatin was used; sometimes one would liquefy the medium 
more slowly, and sometimes another. For example, in one case with 
B. solanisaprus liquefaction began on the third day, and was not com¬ 
plete in 60 days. In another series the same organism, incubated at the 
same temperature, 20° C., showed the beginning of liquefaction in less 
than 24 hours, which was complete in 7 days, or the shortest time ob¬ 
served for any of the series. After Nelson's photographic gelatin, No. 1, 
was adopted, the results were much more uniform. So close were these 
at times that in a series of duplicate or triplicate cultures of the 6 organ¬ 
isms named it would be impossible to pick out those which were of the 
same name, except for the labels on the tubes. 
Therefore the final conclusion was that B . atrosepticus , B. solanisaprus , 
B. melanogenes , and the three organisms from Maine present no well- 
defined differential characters upon gelatin stab which would separate 
them from each other. The observed characters of the six on gelatin 
may be briefly summarized as follows: A needle growth was apparent 
in 12 hours at 20° to 22 0 C. Liquefaction as a rule begins in from 18 to 
24 hours, and may not begin until the third day. It is usually complete 
in about 10 days, but may be delayed for some time longer. Usually 
liquefaction is infundibuliform to slightly napiform and later may assume 
a saccate appearance. Occasionally liquefaction starts off rapidly at the 
surface, giving a distinct crateriform appearance, which is quite likely to 
