Dec. 13. i9ts Angular Leaf-Spot of Ciicumbers 471 



There was a marked reduction of colonics on the plates exposed for 15 

 minutes (estimated, 70 per cent), and 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. XLVII, 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 plates. — On +15 peptone-beef agar at 23° C. surface colonies 2 

 days old are 1.5 to 2 mm. in diameter, round, smooth, shining, slightly convex, finely 

 granular (under the compotmd microscope), with an opaque white center and a thin, 

 transparent, entire margin. When 3 to 4 days old at 23° 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. i). At higher temperatures (27° 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 +15 peptone-beef agar when 2 days old at23° 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 (PL XLIX, fig. 2). Liquefaction is 

 slow (18° to 20° 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. 



