STEWART'S DISEASE OF MAIZE: TYPE 161 



organism is extremely abundant in the vessels and is much 

 inclined to come to the surface of the husks through stomata 

 (Figs. 105, 106, and 107); thus flooding the kernels, but it may 

 occur also inside the kernels, particularly at their junction with 

 the cob (Figs. 108 to 111). Some of the infected plants are de- 

 stroyed in the seedling stage (Fig. 112), but many of them reach 

 a height of several feet before showing secondary signs (Fig. 

 113). It is a typical example of a seed-borne infection. Noth- 

 ing is known as to the occurrence of this disease outside of the 

 United States. Miss Doidge has not seen it in South Africa. 

 The exact distribution of the disease in the United States is un- 

 known but it occurs from New York and Maryland to California. 



Cause. It is due to Aplanobacter stewarti (EFS) McC. 

 This is a non-motile, non-flagellate, non-sporiferous, inadhesive, 

 or moderately viscid, yellow, slow-growing, non-liquefying, 

 non-milk-curdling, non-nitrate-reducing, non-gas forming, non- 

 starch-consuming, chloroform-tolerant, sodium chlorid-tolerant, 

 aerobic, rod-shaped schizomycete, growing on the surface of 

 agar-poured plates in the form of small, flat, circular or nearly 

 circular pale colonies which become yellow with age. 1 It 

 reddens lavender-colored litmus milk slightly and does not 

 grow in Cohn's solution. Its growth on steamed potato is 

 thin and soon at an end (contrast with Nos. II, VIII, or X). 

 Why is this? In Dunham's solution containing methylene 

 blue the bacterial precipitate should be blue. 



Its minimum temperature in +15 peptone beef bouillon 

 is above 9C. At this temperature there was no clouding 

 in 14 days. The checks at room temperature clouded heavily 

 the second day and formed a pellicle the third day. It is not 

 sensitive to dry air, and like No. II retains its vitality and its 

 virulence for a long time. It is rather tolerant of weak organic 

 acids. On the kernels the majority of the bacteria are destroyed 

 by exposure for 15 minutes to 1 :1000 mercuric chlorid water: 



1 Sometimes the surface colonies on agar have depressed centers (Fig. 1145). 

 No mention was made of these in Volume III of my monograph because I was not 

 then certain that they belonged in the life-cycle of this organism, but recently 

 Lucia McCulloch, of my laboratory, has proved them to be infectious. She has 

 also proved my former statements respecting the motility of this organism to be 

 incorrect (see Phytopathology, August, 1918, p. 440). 



