Dec. 13, 1915 
Angular Leaf-Spot of Cucumbers 
47 i 
There was a marked reduction of colonies on the plates exposed for 15 
minutes (estimated, 70 per cent), arid almost complete absence of colonies 
on those exposed for 30 minutes (estimated, 95 per cent destroyed). 
The contradictory earlier result must therefore be attributed to a feebly 
actinic condition of the sky not visible to the naked eye. 
SENSITIVENESS TO FREEZING 
The organism is quite sensitive to freezing. A transfer was made to 
beef bouillon from a 5-day-old bouillon culture, shaken well and allowed 
to stand for five minutes. Plates were then poured with measured loops 
from this culture. The tube was then buried in salt and pounded ice, 
frozen solid and kept frozen for 15 minutes, after which it was thawed in 
cool water (five minutes required), shaken thoroughly, and used for a 
second set of plates, the loops being measured exactly as before. Two 
days after pouring the colonies were counted. There were one-ninth as 
many colonies after freezing as before freezing (PI. XI/VTI, fig. 3). A 
longer incubation (five days) did not increase the number of colonies on 
the plates. 
Thinking that five minutes might not have been long enough to obtain 
a uniform diffusion of the bacteria in the fluid, the experiment was 
repeated, allowing the tube to stand an hour with shaking before the 
plates were poured. The result was practically the same, nine-tenths of 
the bacteria being destroyed by the short freezing, the count being made 
on the fifth day. 
cultural characters 
Agar-poured peates.— On +15 peptone-beef agar at 23 0 C. surface colonies 2 
days old are 1.5 to 2 mm. in diameter, round, smooth, shining, slightly convex, finely 
granular (under the compound microscope), with an opaque white center and a thin, 
transparent, entire margin. When 3 to 4 days old at 23 0 C. the largest measure 4 to 
7 mm. in diameter and the white opaque center spreads in radiating lines into the thin 
margin (PI. XLIX, fig. 1). At higher temperatures (27 0 to 30° C.) they reach this 
size in two to three days. Buried colonies are lenticular. Later (when 4 to 5 days 
old) the surface colonies lose their dense white center and dry down very thin and 
transparent and then show little or no trace of the radiating lines. 
Agar stabs. —Stabs in -j- 15 peptone-beef agar when 2 days old at 23 0 C. show a raised, 
smooth, shining, white, transparent, surface growth 8 mm. in diameter. Growth is 
visible only along the upper one-third of the stab. This is granular, not villous. 
Old cultures have a thin white growth completely covering the surface, and the 
agar is then frequently pale green, fluorescent. 
Agar slants. —On slant agar, stroke cultures make a moderate, thin, white, trans¬ 
parent, smooth, shining growth, denser in the center. There is considerable white 
sediment in the V. 
Gelatin plates. —Surface colonies on gelatin plates show a peculiar margin, best 
seen under low magnifications, with oblique light (PI. XEIX, fig. 2). Liquefaction is 
slow (18 0 to 20 0 C.), and when the layer of gelatin is thin (10 c. c. to a plate) does not 
take place, as the medium soon becomes too dry for growth. On plates containing 20 
c. c. of gelatin liquefaction began on the twelfth day and on the sixteenth day was 
complete, the colonies floating intact in the liquid gelatin. 
