296 



BACTERIAL DISEASES OF PLANTS 



and pear (No. XII), the only subsequent agent necessary 

 being rain or dew. That a considerably greater number of 

 hours of continuous moisture (than under experimental, fresh- 

 culture, hothouse conditions) is necessary to insure infection 

 under natural field conditions, is shown, I think, by Halsted's 

 observation that in a New Jersey bean field nine-tenths of the 

 infections were on the west side of the pods, i.e., on that side 



FIG. 229. Bacterium phaseoli: Buried and surface colonies on an agar poured 

 plate. Idaho isolation. Plate poured August 24, 1914. Photographed August 

 28. X 10. Oblique lighting. 



likely to remain damp longest because shaded from the morning 

 sun. (In this connection read comment on black spot of the 

 plum in "Bacteria in Relation to Plant Diseases," Vol. II, p. 62). 

 Can you verify Dr. Halsted's observations? Do you think 

 that what he saw could have been due to driving rains from the 

 west? In that case the infection should sometimes occur most 

 abundantly on the east side of the pods. Watch for this. 



Barlow proved by transfers to culture media that Bacterium 



