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 iracTieipMlus 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 TROM CUCUMBERS 

 \\2FR0M SQUASH K- 



7 FROM CANTALOUPES 



14 CUCUMBERS v 

 2 SQUASHES x 

 2 CANTALOUPES 



Si Sa.^ .-ICu,^ 

 — ■-*» or -t >■ 



Sq Sq r „ Cu 



DEGREES OF 



Virulence 



B 































§ 



f 



f 



|3§3 | 



f 





A A . ,. 



\.i 



o 



c 

 o 



c 













! 







'l/W\ 



\ 



s 



00 

 Fl 

 7} 



















Fig. 6.— Curves showing the varying degrees of virulence among different isolations of Bacillus track eiphilus 

 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, andSt/refertothesourceoftheisolationasbeing 

 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. tracTieiplittus 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 lli from R 

 230 and En 15 from R 235) were found still to retain approximately 



