Oct. 21, i9i8 Angular-Leafspot of Cucumber 211 



BY DRAINAGE WATER 



Evidence concerning the distribution of the causal organism by 

 drainage water during rains was afforded by comparing developments in 

 fields A and B which were mentioned in the preceding section. The 

 rows in field A ran across the hillside, while in B they followed the direc- 

 tion of the slope (fig. 2). After the rains of July 12, 16, and 19 the dis- 

 ease appeared in field B throughout the length of the rows in which it 

 had been noted earlier and in plots below them where disinfected seed 

 had been planted. In field A, however, the spread of the disease was 

 nol mainly along the rows but rather crossed the rows, following the 

 path of the drainage water. The supposition is that the organisms were 

 carried by the drainage water and from it were spattered by the rain to 

 the healthy plants. Dissemination by drainage water has been noted 

 before with fungus diseases — for example, cabbage-yellows by Jones 

 and Gilman (9)— but, so far as is known to the writer, no evidence has 

 before been published in regard to its significance in the case of a bac- 

 terial disease. 



Attempts to prove that drainage water carried the causal organisms 

 were made on two occasions late in the summer. Samples of drainage 

 water caught during rains at the lower edges of infested fields were 

 taken to the greenhouse and sprayed on healthy plants. The negative 

 results are not surprising in view of the fact that few new infections 

 developed in the fields where the water was caught, and that negative 

 results from attempts to isolate the bacterium from beetles from these 

 same fields also indicated that a large proportion of the bacteria had been 

 killed as a result of the long, preceding period of dry weather. 



BY PICKERS 



The spread of diseases due to fungi has been attributed to pickers — 

 for example, bean anthracnose, by Whetzel (17) — but, so far as the 

 writer is aware, no such fact has been demonstrated for a bacterial dis- 

 ease. Experiments in the case of the cucumber angular-leafspot have 

 shown that the disease may be spread by pickers if picking is done 

 when the exudate is present on the infected leaves. On August 8 and 9, 

 1916, the matter was tested as follows: At 5.30, 7.30, and 8 o'clock on 

 the morning of the first day and at 8 a. m. on the second day two or 

 three leaves in each case were inoculated by rubbing with the hands 

 (as is done by pickers) after having first rubbed them through the 

 exudate on diseased leaves. In all four cases inoculated leaves became 

 infected (PI. 15, B), while the uninoculated controls remained healthy. 



Picking is, of course, frequently done early in the morning and on 



rainy days when the leaves are wet and the bacterial exudate is abundant. 



Numerous observations show that the spread of the disease in the way 



described in the preceding paragraph often results. The most obvious 



78775°— 18 6 



