Oct. 21, i9i8 Angular-Leafspot of Cucumber 205 



exposure the highest temperature was 0° C. (32° F.), the lowest -25.5° C. 

 (-14° F.), and the average daily mean was — i5.5°C. (4.1° F.). One 

 tube of each medium was taken in after 24 hours and longer periods and 

 thawed slowly in cold water. In the salt bouillon all the bacteria were 

 dead after 24 hours. In bouillon without salt all were dead after 60 

 hours. No test was made of the suspension in distilled water after the 

 60-hour interval, but no colonies developed in plates poured from one 

 of the other tubes melted after 4 days. On the agar some of the organ- 

 isms were alive after 6 days, but after 17 days all were dead. The sensi- 

 tiveness to freezing was undoubtedly increased by the sodium chlorid 

 in the bouillon. 



Smith and Bryan (75, p. 471) reported freezing the organisms for 15 

 minutes in bouillon by means of salt and pounded ice. That exposure 

 resulted in the death of nine-tenths of the bacteria. 



SENSITIVENKSS TO GERMICIDES 



Tests of the sensitiveness of the organisms to formaldehyde, copper 

 sulphate, and mercuric chlorid were made. The dilutions of formalde- 

 hyde were made up by volume from the 40 per cent formaldehyde solu- 

 tion known commercially as formalin. The copper-sulphate and mer- 

 curic-chlorid solutions were made up i to 1,000 by weight and the 

 desired dilutions made from these. Exposures were made in all cases 

 by transferring a 3-mm. loop of a young bouillon culture to lo-cc. portions 

 of the dilutions in vials floated on a water bath at 25° C. Tubes of 

 melted agar were inoculated in duplicate or triplicate by a 3-mm. loop 

 transfer from each vial after an exposure of 10 minutes. 



The test with formaldehyde resulted in the death of all organisms ex- 

 posed to a dilution of i to 10,000, of nearly all in the i to 100,000 dilution, 

 and of apparently none in the i to 500,000 dilution. The tests with cop- 

 per sulphate and mercuric chlorid were repeated twice. With the copper 

 sulphate the results did not agree throughout, but in all cases all organ- 

 isms were killed or prevented from developing by the i to 100,000 dilution. 

 There were no colonies, or a strikingly smaller number than from the con- 

 trols, in the plates poured from the i to 500,000 dilution. All organisms 

 were killed by exposure to dilutions of mercuric chlorid of i to 1,000,000. 

 The sensitiveness of the organism to copper sulphate was tested by 

 Smith and Bryan (15, p. 474). Their results show a slightly less marked 

 sensitiveness to this chemical than was found in the tests made by the 

 writer. The temperature at which their exposures were made was not 

 stated. 



PLANTS ATTACKED 



Little attention had been previously given to the question of the host 

 range of the disease or to the question of variations in susceptibility or 

 resistance to the disease in the case of the different types of cucumbers. 



