July 15, 1924 
Bacterial Pustule of Soybean 
67 
mesophyll, may be involved. The 
physiological phenomena which attend 
these hypertrophic changes are de¬ 
pendent no doubt upon certain enzy¬ 
matic activities which involve both the 
cell walls and the cell contents. The 
parasite and host relationship and thus 
the proximate cause of pustule forma¬ 
tion is believed to be analagous to 
that which obtains in the case of 
citrous canker caused by Pseudomonas 
citri (15). In the case of this organism 
evidence has been advanced that both 
cytolytic and diastatic enzyms are 
secreted. Through their activity these 
modify the osmotic properties of in¬ 
vaded cells and thereby are responsible 
for their enlargement. 
ion is supported by the fact that it has 
been impossible to separate the soy¬ 
bean organism from bean blight mor¬ 
phologically and culturally. It seems 
advisable, therefore, to regard the 
soybean organism as a variety of Bad . 
phaseoli. 
RELATION OF PARASITE TO HOST 
TISSUE 
Lesions which were appropriately 
fixed in alcohol, embedded, sectioned, 
and stained with alcoholic methylene 
blue were employed in histological 
studies. Entrance of the parasite is 
very manifestly effected through the 
stomates which occur on both leaf 
Fig. 4.—Invasion of substomatal cavity by Bad. phaseoli var. sojense 
surfaces, as evidenced by the fact that 
the substomatal chamber and the 
intercellular spaces of the tissues 
immediately surrounding the stomata 
in the case of young lesions are densely 
filled with bacteria (fig. 4). In the 
older lesions, after the host cells have 
collapsed, the bacteria are not confined 
to the intercellular spaces, but occur 
within the cell cavities. These phe¬ 
nomena are entirely in accord with 
those known to occur in the case of 
nearly all plant bacterial pathogens 
which invade parenchyma. So far as 
pustule formation is concerned, how¬ 
ever, the writer's observations are not 
in agreement with the statement made 
by Miss Hedges (4) that the pustules 
show both hypertrophy and hyper¬ 
plasia. The preparations in hand 
show that these elevations arise wholly 
from hypertrophy and without hyper¬ 
plasia. Any or all of the tissues, 
epidermal, palisade parenchyma and 
RESUME OF SALIENT CHARACTERS 
On the basis of the foregoing studies, 
Bad. phaseoli var. sojense is a rod¬ 
shaped organism occurring singly, in 
pairs, or catenulately. The cells meas¬ 
ure 1.3 to 2.0X 0.6 to .75 m, are motile 
by means of a single polar flagellum, 
possess no - well-defined capsule nor 
endospores, are strictly aerobic and 
Gram-negative. Colonies on nutrient 
agar are circular, raised, smooth, shiny, 
yellow and have an entire or slightly 
lobed margin. The organism is ca¬ 
pable of liquefying gelatin and blood 
serum, digesting casein and asparagin, 
is strongly diastatic, very resistant to 
drying, nonnitrate reducing, and forms 
neither acid nor gas from the various 
carbon compounds. Its thermal death- 
point is approximately 50° C. It has 
not been possible in culture to dis¬ 
tinguish it from Bad. phaseoli. Ac¬ 
cording to the 1920 descriptive chart 
