572 BACTERIA OF PLANT DISEASES. 



which ooze out when the stein is cut across. The foliage may wilt with or 

 without a preliminary yellowing 1 . If the bacteria are abundant in the ves- 

 sels of the stem, the wilt is often very sudden and the foliage has no time to 

 become yellow. The progress of the disease seems to be more rapid in young 

 than in old plants and in hot than in cold weather. 



"In the case of the potato the tubers are also finally attacked and de- 

 stroyed, the organism reaching them by way of the vascular bundles of the 

 stem. A brown or black rot ensues, beginning in the stem end of the tuber 

 in the vascular ring and extending in all directions therefrom. All stages 

 of this rot of the tubers (both in 1895 and in 1896) were obtained repeatedly 

 from pure cultures of the bacillus pricked into the stem several feet above 

 ground. 



" Bouillon and Peptone Cultures. This organism grows well at room 

 temperatures of 20 to 30 C., in beef broth peptoiiized (Witte's peptonum 

 siccum). It seemed to make little difference whether the bouillon was left 

 acid or rendered slightly alkaline with carbonate of soda. The gathering of 

 the zooglcea in the upper layers of the fluid is very distinct, especially if the 

 tubes are left undisturbed in an upright position for some days. On shaking 

 the turbidity becomes uniform. The organism produces a copious, dirty 

 white precipitate (much more precipitate than B. tracheiphilus). 



"The inoculated tubes of litmus milk developed no acid i.e., showed 

 no trace of reddening. After two or three days the litmus became perceptibly 

 bluer than in the control tubes, and this bluing increased from day to day, 

 indicating a progressing alkalinity. This change took place at room tem- 

 peratures of 20 to 30 C., and also in the thermostat at 37 C. The casein 

 was not precipitated. 



" Gelatin. In plate cultures of nutrient gelatin the buried colonies are 

 circular in outline (globose), yellowish or brownish, granular (under Zeiss 

 sixteen millimetres objective and 12 compensating ocular), and with well- 

 defined margins. No oblong or spindle-shaped colonies could be found. 

 The circular outline and regularity and distinctness of the margin of the 

 colony were especially noteworthy. Whether these features will be found 

 constant with all gelatins is a question yet to be determined. Occasionally, 

 after a few days, a narrow, clear zone appeared around the margin of many of 

 these colonies as if liquefaction had set in. This, however, did not progress, 

 or increased but very slowly, and was clearly visible only under the compound 

 microscope. The buried colonies remained small, as if requiring more 

 oxygen than they were able to get. The surface colonies were circular, thin, 

 thin -edged, smooth, white, and wet-shining. They did not spread over the 

 plate rapidly or cause any liquefaction (fifteen per cent gelatin, temperature 

 20 to 27 C.). 



"The organism grew best in a gelatin of the following composition: 

 Lean minced beef, five hundred cubic centimetres ; distilled water, one thou- 

 sand cubic centimetres ; mixed and set twenty-four hours in a cool place ; 

 filtered and added ten grammes of Witte's peptonum siccum and one hundred 

 and fifty grammes of L. and F. gelatin. This gelatin was clarified with egg 

 and rendered alkaline with sodium hydrate, titrating with phenolphthalein. 

 The degree of alkalinity was between twelve and fourteen of Mr. Fuller's 

 scale. 



"Agar. In poured plates of nutrient agar the buried colonies differed 

 considerably from those in gelatin. Instead of being circular with a very 

 smooth margin, they were irregularly round or even oblong, with a decidedly 

 irregular granular margin. These colonies were brown or yellowish-brown 

 under sixteen millimetres objective and 12 ocular. After some weeks the 

 whole body of the agar became decidedly brown. No spindle-shaped colonies 

 were to be seen The surface colonies grew rather slowly. They were dirty- 

 white, smooth, wet-shining, and did not spread widely over the agar. 



' * The behavior on potato is very characteristic. In twenty-four to forty- 

 eight hours (temperature 27 to 32 C.) the fluid became turbid and the pro- 



