28 
BULLETIN 828, U. S. DEPARTMENT OF AGRICULTURE. 
the wilting of one to several leaves, but never caused wilting of an 
entire plant. Of this group, 14 isolations were from cucumber, 2 from 
squash, and 2 from cantaloupe. The third and last group, made up 
of 23 isolations from cucumber, 2 from squash, and 7 from cantaloupe, 
falls upon virulence index zero — that is, none of these isolations gave 
any apparent infection at all on White Bush Scallop squash, although 
all had caused infection in cucumber. In cases of recovery of a squash 
plant after partial wilting, Bacillus trachei'pMlus may continue to live 
in the vascular tissue of the apparently healthy plant. In one such 
instance plates were poured from the fruit of an inoculated squash 
plant about one month after apparently complete recovery from wilt, 
23 FROM CUCUMBERS 
FROM SQUASH tf- 
FROM CANTALOUPES 
14 CUCUMBER^™ 
2 SQUASHES Nk 
2 CANTALOUPES \ 
degrees of 
Virulence 
jj sjfcWk 
B 
f f 
1 
7? 77 '• 
5 
2 £«ssg 
A A . ,, 
1 s 
c 
o 
c 
1 
il l! 
!j Ji 
1 III \j 
\Av\ 
i 
s 
CO 
rn 
73 
o 
.0 5 
5 
2 
V> 
z 
I 
5 
so 
S? 
10 5 
Fig. 6.— Curves showing the varying degrees of virulence among different isolations of Bacittustracheiphilus 
from the three common hosts and from many sections of the country as demonstrated by large numbers of 
inoculations into squashes (A) and into cucumbers (B), 62 different isolations being tested in this way 
on squashes and 103 on cucumbers. Theletters Cu, Ca, and S<7 refer to the source of the isolation as being 
cucumber, cantaloupe, or squash, and the figures preceding refer to the total number of isolations from 
each host possessing a similar degree of virulence. 
and B. tracheiphilus was recovered from these plates and proved 
infectious by inoculation into cucumber. 
A large proportion of all the isolations were retested on both cucum- 
ber and squash in April, 1918, and essentially the same relations have 
continued to hold after long periods. For example, two isolations 
(R 230, New York; R 235, Michigan) from cucumber carried contin- 
uously in culture since August, 1914, and tested from time to time by 
inoculations, have preserved approximately the same virulence to 
Chicago Pickling cucumber and the same relation to each other during 
all this time, R 230 being considerably more virulent than R 235. 
Furthermore, in 1915 these two isolations were inoculated into cu- 
cumber plants and then reisolated. The reisolations {En 11+ from R 
230 and En 15 from R 235) were found still to retain approximately 
