Some Potato Diseases. 



309 



to the position of the vascular bundles, will be seen. These brown 

 streaks are the vessels crowded with bacteria, which gradually 

 descend the stem and finally pass into the tubers, where they 

 first manifest their presence by a more or less interrupted pale 

 brown zone, situated some little distance from the outside of the 

 potato. This zone corresponds to the position of the vascular 

 bundles in the tuber. As the bacteria multiply the coloured 

 zone becomes darker, and finally blackish, at the same time 

 extending towards the centre of the tuber, which eventually 

 becomes rotten, the skin alone resisting the disintegrating action 

 of the bacterium. 



According to Dr. E. F. Smith, infection usually takes place 

 through the leaves or stem, the parasite gradually working down- 

 wards until it reaches the underground tubers. Furthermore, 

 minute insects of various kinds are supposed to be the 

 main agents in causing a widespread epidemic, by alternately 

 feeding on diseased and healthy plants. It is probable that 

 underground infection may also occur from bacteria present in 

 the soil. 



Tomatoes and egg-plants also suffer severely from this disease 

 in the United States. 



Preventive Measures. 



The important point to attend to is the destruction of insects 

 that feed on the leaves of the potato. This can be accomplished 

 by spraying with Bordeaux mixture to which an insecticide has 

 been added. 



If potatoes are dug as soon as the disease is indicated by the 

 wilting of the leaves, a considerable portion of the crop may be 

 saved by storing the tubers in a cool dry place. If allowed to 

 remain in the ground, not only do the tubers become rotten but 

 •the soil is also badly infected. 



Potatoes or tomatoes should not be planted in soil that has 

 produced a diseased crop, nor should potatoes from a diseased 

 area be used for " sets." 



Fuller details of the bacterium, and of the wholesale destruc- 

 tion caused by its presence in the United States, will be 

 found in " A Bacterial Disease of the Tomato, Egg-plant, 



