Apr. 19, 1924 
Bacterial Leaf spot of Delphinium 
265 
CULTURAL CHARACTERS 
Beef agar plates. 5 —Colonies are visible on the second day and by the third 
day in thin sown plates are 3 to 5 mm. wide, round, white, transparent, opales¬ 
cent, slightly convex, sometimes slightly umbonate, smooth shining, finely 
granular. Young colonies show coarse cross-hatching by oblique transmitted 
light (PI. 4, F and G) and sometimes these internal cross-hatchings persist in 
the older colonies at summer temperatures but usually they give place to internal 
concentric markings (PI. 4, E). Buried colonies are lenticular. When older* 
the colonies may reach a diameter of 8 mm. The consistency is sometimes 
slightly viscid. Occasionally a ring of irregular opaque areas or radiating lines 
may appear in the colonies (PI. 4, D) and old colonies may become slightly 
lobed. Plates from old litmus milk and from old bouillon cultures have given 
very convex colonies with depressed centers which, as they enlarge, have a 
wrinkled surface. After return to favorable cultural conditions, transfers from 
these colonies again gave normal colonies on agar plates. 
Beef agar slants. —Growth is thin, white, smooth shining, transparent, 
opalescent, with internal wavy markings and entire margins. Growth does not 
cover the surface but tapers upward from a width of 3 to 6 mm. There is con¬ 
siderable white precipitate in the V. Numerous small crystals form beneath 
the growth and the agar becomes green. 
Potato cylinders. —The moderate, thin, spreading growth on potato cylinders 
is dirty white becoming pale tan colored, with a slimy consistency; the potato 
begins to gray in 24 hours and in a few days is gray throughout. There is no 
distinct odor. Starch is only partially digested, i. e., a purple color is produced 
by adding iodin to the crushed potato cylinders on which the organism has 
been growing. 
Starch agar plates. —Smears were made on starch agar poured plates from 
young agar cultures. When tested after 7 days by drenching the surface of the 
plate with iodin solution an area 5 to 8 mm. wide surrounding the growth was 
purple in color but there was no area of complete starch destruction. 
Whey agar. —On whey agar titrating +8 or P H 7.4 colonies are very convex, 
creamy white, opaque, round with entire margins, not opalescent, with internal 
concentric markings in the margins and in thin sown plates are 5 to 7 mm. wide 
when 10 days old. 
Beef bouillon. —Clouding occurs near the surface in 24 hours with a delicate 
pellicle which falls readily in fragments on being disturbed. Undisturbed 
cultures 2 days old are well clouded throughout and have a heavy pellicle, borne 
down in the center with a mass of white growth, giving the appearance of gelatin 
liquefaction (PI. 4, H) when viewed from the side, but from the top showing a 
nail-head of white in the center of the membranous pellicle. This pellicle falls 
readily as a whole on shaking. Disturbed cultures re-form their pellicle quickly 
when young but not after the cultures are 6 or 8 days old. Blue-green fluorescence 
begins at the top in young cultures. Old cultures are green throughout. 
Beef gelatin plates. —In+ 10 (P H 7.2) beef gelatin, kept at 20 to 22° C., 
colonies on the second day are minute white spots lying in shallow pits of lique¬ 
faction several times their width. By the fourth to the sixth day colonies may 
reach a diameter of 1 cm., clouding the liquefied gelatin uniformly except for a 
heavier mass of growth at the center. 
Beef gelatin stabs. —Liquefaction begins on the second day (20 to 24° C.) 
and is napiform, becoming stratiform. Liquefaction is complete in two to three 
6 All beef media used were made with beef infusion plus 1 per cent Difco peptone. Titrations expressed 
by + and — are according to Fuller’s scale. 
