94 



pine apple, oranges, Satsumas or seedling trifoliate or- 

 anges. Successful inoculations were made by spraying 

 the trees with a bacterial suspension obtained from 

 pure cultures, plate 2, fig. 5, by immersion of the 

 leaves in such suspensions, plate 2, fig. 3, bj' transfer- 

 ring the bacteria into the tissues through needle punc- 

 tures, or by rubbing the leaves between the thumb and 

 fingers after having dipped them in a suspension con- 

 taining bacteria. 



The period of incubation appears to vary, depend- 

 ing on temperature, moisture, and age of the plant 

 tissues. The disease may be evident to the unaided eye 

 three daj^s after inoculation in some cases and ten days 

 may be required in others. The most rapid develop- 

 ment of the disease occurs under humid conditions, on 

 young tissues. Mature parts, however, may become 

 diseased. The illustrations, representing natural and 

 artificial inoculations in Miss Hasse's report, differed so 

 materiallj'^ and the latter were so unlike aitything 

 which had ever come under the writer's observations 

 that no explanation of the differences could be made 

 at first. When, however, inoculated plants were kept 

 under bell jars in a saturated atmosphere cankers rep- 

 resented in plate 2, fig. 2. were formed which are re- 

 garded as similar to the artifical infections produced 

 by Miss Hasse, plates IX and X. 



Pscudomonas citri is a yellow, rod-like organism 

 about three or four times as long as broad. It occurs 

 singly or in chains of six or more elements. The or- 

 ganism possesses a lash-like process which enables it 

 to move about in liquids. It grows readily in culture 

 on a variety of artificial media. It is capable of with- 

 standing somewhat higher temj)cratures than many 

 other bacteria which cause plant diseases. Stevens (4) 

 found that the bacteria can be killed at temperatures 

 ranging from 55-60 degrees C. Tests conducted under 

 other conditions by the writer led to the conclusion that 

 the thermal death point of Pseudomonas citri is about 

 65 degrees C. It is believed to be rather resistant to 

 drying since it retained its vitality for about two months 

 on microscopic slides placed in moist chambers. 

 Stevens (4) found that it did not survive exposure on 

 glass slides for two weeks under laboratory conditions. 



(4) Stevens, II. E. Citrus canker, III, I'la. Agr. Exp. Sta. BulL 

 128: p. 3-20; flgs. 4, 1915. 



