384 



[Vol. 9 



UK 



A large number of varieties of various cereals are subject 

 to attack. Artificial inoculations also indicate that the or- 

 ganism is capable of doing serious damage, particularly to seed- 

 lings of oats and barley. 



Lesions on foxtail appear as light brown or dark brown spots 

 and streaks of no definite size or shape and may occur on any 

 part above ground, but are most often found on blades and 

 sheaths. 



Attacks on other hosts vary from light yellow indefinite areas, 

 often with a reddish tinge in the case of oats, to grayish -green, 

 markedly withered areas. 



The disease appears to be different from any other known bac- 

 terial disease of grasses. 



Attacked tissues teem with bacteria which discolor, disinte- 

 grate and finally kill the invaded tissue. Entrance to the host is 

 by means of stomata and water pores. 



The organism is a single-flagellate rod, white in culture, with 

 colonies surrounded by a characteristic colorless area followed by 

 a white precipitate on slightly acid media. It is described as 

 P seudomonas alboprecipitans n. sp. 



The meaning of hydrogen-ion concentration, its relation to 

 titratable acidity, methods of measuring it, and the necessity of 

 utilizing it in the study of bacterial pathogens are discussed. 

 Comparisons are given between Fuller's scale and P H values. 



Numerous cultural reactions are presented, including a method 

 for definitely controlling precipitate production by means of 

 varying the hydrogen-ion concentration ; the relationship of var- 

 ious organic anions to growth, comparison between cotton and 

 glass wool as filtering agents, the use of lima bean agar in bac- 

 terial studies, and a study of several amino acids in relation to 

 growth of bacteria are also discussed. 



It is found that beef extract is the probable source of the 



white precipitate in media which contain the extract and that this 



precipitate is a phosphate. 



Part of the work presented in this paper was prosecuted as an 

 Adams project at the Agricultural Experiment Station of the 

 University of Arkansas. Special thanks are due to Dean Bradford 

 Knapp for facilities made available and to Dr. J. A. Elliott who 

 made the colored drawings and who gave kindly assistance and 

 encouragement in the prosecution of the work. The work was 

 continued at the Missouri Botanical Garden under the guidance 



