140 Dale . — A Bacterial Disease of Potato Leaves . 
spores stain a deep red; many of the Bacteria stain green, perhaps 
because the red colour was washed out in the course of preparation of the 
slide. 
In comparing sections of sterilized (boiled) tuber with those of living 
tuber, it is suggestive that in the former the walls of the host do not stain 
red in the parts attacked by Bacteria, as they do in the latter. The expla- 
nation seems to be that in the living tuber the middle lamella is first 
attacked and dissolved by the organism, and then the cell-wall itself, whereas 
in the sterile tuber the isolation of the cells is brought about, before infection, 
by the process of steaming. Thus the organism finds a path already 
opened. 
On potato extract in gelatine the organism grows well and liquefies the 
gelatine slowly. In a streak culture it first liquefies the part below the 
streak, forming a deep channel down which the culture slips into the liquefied 
medium at the base of the tube, where it proceeds to liquefy the remaining 
gelatine. The completion of the process takes days or even weeks in a low 
room-temperature. 
On potato extract in agar , especially in an incubator at about if C. (the 
ordinary temperature of the laboratory in winter being low), the organism 
grows well. The cultures were slimy, as in gelatine, and pulled out into 
strings. As this medium dried up rather soon the growth ceased. 
On ‘ Lemco ’ beef bouillon in gelatine at a somewhat low ordinary 
temperature (about if -if C.) the organism grew well. The gelatine was 
slowly liquefied, at first along a groove as in potato gelatine cultures. The 
liquid part of the culture was turbid and contained flecks of pellicle. 
In a stab culture a large circular mass of Bacteria was formed, thick in 
the centre and thin at the edges. Growth also occurred, but not very 
abundantly along the line of stab, the separate colonies each appearing as 
isolated round dots. 
In the incubator, at 25° C., a good growth was obtained in liquid 
gelatine, the organism falling to the base of the tube as a whitish precipitate. 
A thin pellicle was formed on the surface. This film broke up and sank 
when the tube was shaken. 
Wood ashes in agar , at i2°-i5° C. 
Streak culture. There was a considerable growth in all the cultures 
made. 
Stab culture. A fair growth was formed along the line of stab, but 
there was no special development on the surface. The organism spread 
along the line of stab in wavy films or cloudy masses, which are very 
characteristic, and quite different from the isolated colonies formed in 
Lemco, and in cane-sugar and peptone gelatine. The difference seems to 
be due to the medium, isolated colonies being formed in gelatine, and wavy, 
cloudy growths in agar. 
