THE BACTERIA.L BLIGHT 165 



Careful inspection shows that their upper surfaces are 

 more or less roughened by darker areas rising above the 

 dead gray tissue. The spots gradually enlarge, and 

 finally run together to form large brown patches, the 

 intermediate tissues becoming yellowish or sickly green 

 in color. The entire plant finally withers, and dies long 

 before the proper period, the tubers being small — gen- 

 erally less than half full size. But the tubers do not rot 

 and are of good quality. This fungus has proven diffi- 

 cult to study in the field, the spores being produced 

 only on part of the affected plants. It Avinters over in 

 the spore stage on the dead vines. 



The Bacterial Blight 



Besides the two maladies already discussed, there is 

 a potato disease due to bacteria, although it is probable 

 that the Macrosporium blight has frequently been attrib- 

 uted to these organisms. Bacteria often develop in 

 tissues invaded by the fungus just named ; but there are 

 good reasons for believing that a genuine bacterial 

 trouble frequently develops in all parts of the plant. It 

 generally starts from the seed planted, which becomes 

 rotten. The vines die prematurely, often wilting rather 

 suddenly, and the young tubers decay. This disease is 

 more troublesome in southern latitudes than at the 

 north. 



Treatment of Potato Diseases. — A large num- 

 ber of experiments in many sections of the United States 

 have shown that these various maladies may be jire- 

 vented by spraying with the Bordeaux mixture. It has 

 been repeatedly shown that vines thus sprayed remained 

 in a healthy normal condition long after the untreated 

 vines were dead, and that, consequently, the tubers 

 developed to a much larger size, with a greatly increased 

 yield. The results of an experiment of this kind, at 



