BLACK ROT OF CRUCIFEROUS PLANTS. 319 
steamed in water the formation of the brown pigment was very decided, finally approxi- 
mating bistre or mummy brown. Harding observed a similar prompt browning in cultures 
made on white winter radish and on cauliflower. Non-cruciferous substrata so far as tested 
do not give any such deep brown pigmentation. 
Colonies of this organism on agar or gelatin are smooth, wet-shining, pale yellow, round, 
flat to convex (Harding), thinning out to a distinct entire margin (fig. 128). The surface 
colonies at first are often quite pale, becoming yellower with age. Buried colonies do not 
develop speedily, neither is the surface growth very rapid; Harding says—rapid at 28° C. 
Feathery X-shaped crystals of ammonium magnesium phosphate are formed after some 
days in cultures on peptonized beef-broth-agar (fig. 128). On +15 nutrient agar after 
a time a white chemical halo forms 
around the colony, streak, or “‘nail 
head”’ of the stab. This appears to 
be common, however, to various 
species of Bacterium. So also are 
the crystals. 
On meat-extract-peptone gela- 
tin, Hecke describes the young col- 
onies as small, cloudy, colorless, 
circular drops which became plainly 
yellow with age and feebly zoned 
concentrically, the gelatin liquefying 
slowly. At his room temperature 
(15° C. ?) the growth on this medium 
was slow, the surface colonies on a 
plate 15 days old measuring only 
about 3 mm. in diameter in a 
liquefied zone 7 mm. in diameter. 
Ont neutralized kohlrabi-gelatin simi- 
lar results were obtained. On the 
contrary, in non-neutralized kohl- 
rabi-gelatin growth was extraordi- 
narily slow, so that the colonies were 
not visible until after the tenth day. 
In my +10 nutrient gelatin, in 
rather thin sowings in Petri-dish Fig: 119.4 
poured-plates, at the end of 7 days, at 
10° to 20° C., the surface colonies of Bacterium campestre under the Zeiss 16 mm. objective 
and 12 ocular were small, circular; and homogeneous (fine granular), with entire margins; 
the buried colonies were globose-lobulated and less than 1 mm. in diameter. 
Bacterium campestre isolated by the writer from a cabbage leaf in June, 1908, on a thin- 
sown agar plate (10 colonies) gave thin, flat, pale yellow, circular surface colonies with a 
slight tendency to rings laut no other distinct naked-eye structure. At the end of 4 days 
at 28° to 30° C., the largest colonies were 8 to 10 mm. in diameter, the surface smooth and 
wet-shining. With Zeiss 16 mm. apo., and 12 ocular the margin of the colonies showed no 
special characteristics. Under this magnification the colonies were uniformly fine granular 
except the extreme margin which was a little paler and nearly amorphous in structure. In 
a plate of the same lot containing about 100 colonies, the surface colonies on the fourth day 
*Fic. 119.—Cross-section of a rape petiole attacked by Bacterium campestre. Plant inoculated Dec. 19, 1896. 
Leaf fixed in alcohol Jan. 9, 1897. Bacteria restricted to the bundles, 7. ¢., to heavily shaded parts, except on right side 
near periphery where intercellular (shaded) spaces are occupied. Drawn from a photomicrograph made with a planar 
lens, from a stained microtome (paraffin infiltrated) section. Actual diameter about 2mm. Slide 107 A. 
