5o8 Journal of Agricultural Research voi. xiii, no. lo 



kind of healthy seed to serve as a control. Each of these rows was no 

 feet long. No blackleg showed in the plants during the growing season, 

 and at digging time, September lo, the tubers were healthy and normal 

 in every respect. 



A similar experiment was carried out at Norfolk, Va.^ Half a 

 barrel of artificially infected tubers were thoroughly rotted by the 

 blackleg organism before they were placed in the soil. There is no 

 question that the bacteria were introduced into the soil in large numbers. 

 The following spring when the potatoes were planted, some of the rotted 

 tubers were still to be found in the soil. No blackleg appeared through- 

 out the course of the experiment. 



As supplementary tests to ascertain whether the organism still re- 

 mained alive in the soil where the diseased tubers were planted, in each 

 of the three experiments mentioned above isolations were made from the 

 tubers themselves and in two of the experiments from the soil imme- 

 diately surrounding the tubers. Many series of these isolations were 

 made from various parts of the plots, and a great number of bacteria 

 were obtained. All of these were tested for their ability to produce 

 blackleg by innoculating healthy, growing plants and cut slices of healthy 

 tubers. As a control for these inoculations, two different strains of 

 authentic cultures of blackleg were used. The results of this work 

 showed that the bacteria isolated from the soil were unable to produce 

 the disease, while the two control cultures did produce the typical 

 blackleg symptons. 



In no case, therefore, was the blackleg organism found to live over a 

 winter in the soil or in the tubers remaining in the soil. Morse ^ says : 



Observations in Maine indicate that under the climatic conditions which exist 

 there infected seed potatoes are the sole source of infectiorwand distribution and that 

 the disease does not live over the winter in the soil. 



In order to get an idea as to whether the results described above are 

 normal, or whether the winter of 191 6 was unusually severe, data in 

 regard to the temperature, amount of snowfall, and total precipitation, 

 were collected for three consecutive winters, as shown in Table I. Ex- 

 amination of this table shows that the winter of 191 5-1 6 was not an 

 unusual one. The average mean minimum and maximum during that 

 season was slightly less than for the winter of 1 914-15 but more than 

 for that of 191 3-14. The snowfall in inches in 191 5-1 6 was consid- 

 erably more than in 1 914-15 and only slightly less than during 

 1 91 3-1 4. This data would seem to indicate that the blackleg organism 

 under the winter conditions that exist in northern Maine cannot survive 

 in the soil or in the diseased tubers remaining in the soil. 



1 The work at Norfolk was done in cooperation with the Virginia Truck Experiment Station and was 

 in charge of Mr. J. A. McClintock. 



2 Morse, W. J. Op. ot.. p. 91. 



