Oct. 8, 1921 Blackleg Potato Tuber-Rot under Irrigation 85 



final sterilization of +20 and —20, Fuller's scale, but not in those 

 adjusted to +30 or to —30. Uninoculated tubes held as controls and 

 titrated at the close of a 24-day incubation period showed marked 

 changes from the original reaction, due doubtless in considerable measure 

 to the absorption of gases with resulting chemical change. Tubes cal- 

 culated for an initial reaction of -f 30 showed a final reaction of from +20 

 to +25; those originally +20 were about +15; those —30 were about 

 — 10; and those —20 were about —6. Transfers from inoculated tubes 

 calculated for an initial reaction of + 30 and above and — 30 and below 

 made 24 days after inoculation developed growth in some cases in tubes 

 from + 30, but not in those from more acid reactions nor from the alka- 

 line broths. 



Vitality on culture media. — ^Long on bouillon, but still longer on 

 agar. 



Temperature relations. — In freshly inoculated broth cultures 

 exposed 10 minutes, occasional retardation of clouding began at 45° C. ; 

 occasional growth was noted at various points between 46° and 50°; 

 and in no case was growth present after heating above 50°. Optimum 

 temperature for growth about 25°. Maximum temperature for growth 

 between 33° and 35°. Minimum temperature for growth below 5°. 



Effect of sunlight. — Thinly sown agar plates exposed on ice for 30 

 minutes the latter part of March in Washington, D. C, resulted in 100 

 per cent killed. 



Cytase production. — Five-day-old 30-cc. broth cultures in 300-cc. 

 Erlenmeyer flasks were precipitated by 160 cc. of 80 per cent alcohol, 

 filtered, and the precipitate dried promptly in the air. The papers con- 

 taining the dried precipitate were washed with 30 cc. of water, and the 

 washings were received in a flask to which a few drops of toluene and three 

 raw Irish potato disks 15 by 2 mm. were added. The disks gradually 

 assumed a soft, cheesy consistency but did not entirely disintegrate. 

 Microscopic examination showed the cells had lost coherence through 

 softening of the middle lamella. The cellulose lamella and the starch 

 content of the cells showed no evidence of change. Controls with 

 uninoculated broth did not soften the disks. 



GROUP number 22 1. 1 II 3033 



The last three points in this group number differ from those given by 

 Morse (5) but coincide with the respective figures in Jennison's {3) 

 revision, as reported by him at the fourth annual meeting of the Pacific 

 Division of the American Phytopathological Society. The writers feel, 

 however, that this may be largely a matter of interpretation of certain 

 results and not necessarily an indication of actual difference in the 

 organisms. Jennison studied 12 different strains of the blackleg bacillus, 

 includingseveralof Morse's strains; but the results he obtained, apparently, 



