1922] 



ROSEN — A BACTERIAL DISEASE OF FOXTAIL 341 



withered areas. On barley and on corn very light yellow or 

 whitish streaks are not uncommon. Barley seedlings, as well as 

 oats, succumb very readily (see pi. 26, fig. 2). 



On millet the attack is usually in the form of grayish green, 

 withered areas, occasionally with brown tinges. On various va- 

 rieties of sorghum the spots are often grayish green bordered by 

 a red band or merely a small red, irregular spot ; reddening, it may 

 be noted, being a much more general character of various sor- 

 ghum diseases. 



There are two diseases of foxtail which are of common occur- 

 rence in Arkansas as well as in other states, notably Delaware, 

 Missouri, New York, and Pennsylvania, which may be mistaken 

 for the bacterial disease. One of these is caused by Cercospora 

 Setariae Atk. and the other is a Piricularia spot. The Cercospora 

 attack is usually in the form of elongated dark brown streaks 

 which usually exhibit the spore groups and thus are easily iden- 

 tified, while the Piricularia spot is usually roundish, light brown 

 in color with a darker brown edge. These Piricularia spots may 

 readily be confused with the bacterial spot because of their close 

 resemblance and because the spores are often difficult to find. 



Microscopic examination will, however, usually bring out the 



difference. The bacterial spots are full of bacteria which in a 

 water mount with slight pressure will stream out of the tissues 

 in the form of dense, grayish white clouds. They may also be 

 detected within the cells. Rarely are bacterial spots contami- 

 nated by fungi. 



INTERNAL APPEARANCE AND PATHS OF INFECTION 



Sections of diseased leaves show the bacteria present in great 

 numbers within the cells and in the intercellular spaces (see 

 pi. 27, fig. 1). The parenchyma is apparently the only part at- 

 tacked, since no bacteria have been observed within the bundles. 

 The attacked cells lose their turgidity, suffer partial or complete 

 collapse, are more or less disintegrated, and variously discolored. 

 Externally the collapse of cells is indicated by a shrinking and 

 withering and finally by splits or breaks in the diseased parts. 

 Ordinarily there is no oozing outward of bacteria, but under very 

 moist conditions and where rifts have occurred in the tissues the 

 bacteria are present in great numbers in the drops hanging to the 

 rifts. This undoubtedly leads to the dissemination of the patho- 

 gen by rain and by winds. (Spreading by insects is also to be 

 expected.) 



