572 BACTERIA OF PLANT DISEASES. 
which ooze out when the stem is cut across. The foliage may wilt with or 
without a preliminary yellowing. If the bacteria are sharia 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. Al] 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. 
‘*Boutllon and Peptone Cultiures.—This organism grows well at room 
temperatures of 20° to 30° C., in beef broth peptonized (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 zodglcea 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 Iitinws 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, 
aftei™ few days, a narrow, clear zone appeared around the margin of many of 
these colonies as if liquefaction had setin. 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 ege 
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- 
