852 
Journal of Agricultural Research 
Vol. XXXI, No. 9 
organism was isolated also from lima beans grown in home gardens 
and from those exposed to infection in the experimental plots at the 
Purdue Experiment Station. 
For the subsequent detailed study three strains were used, one an 
isolation from a cowpea-leaf lesion made August 26, 1921, and two 
were reisolations made in September, 1921, from cowpea-leaf lesions 
produced by field inoculations. These strains were tested for purity 
by poured plates and for pathogenicity by inoculations. 
MORPHOLOGY 
The organism is a rather small rod with rounded ends, and occurs 
singly or in pairs. The rods stain more readily in gentian violet than 
in ZiehTs carbol fuchsin or rose bengal. In agar cultures 24 hours 
old the cells varied in width from 0.44 to 0.66 /*, and in length from 
1.10 to 2.34 ijl, with an average of about 0.54 by 1.47 m- 
To obtain actively motile cells for the flagella stain, a piece was cut 
out of a 48-hour-old culture on potato-dextrose agar at the base of 
the slant and dropped into a sterile water blank. After four hours 
an examination of a hanging drop showed an abundance of motile 
cells and indicated that tne organisms had diffused throughout the 
liquid. Smears were made from this water culture, and the flagella 
were stained by Van Ermengem’s method. One to five flagella were 
found at one or both poles. Considerable variation was found, but 
more frequently there were three or four flagella at one pole and 
fewer at the other. Five flagella were noted at each pole in some 
instances. In another culture the predominating condition was that 
of one or two flagella at only one end of the rod. A few flagella were 
measured an<^ ^eraged 6.5 /x in length. 
Endospores, capsules, and involution forms have not been noted. 
In water suspensions 30 hours old the cells become swollen and 
vacuolated. The organism is gram negative. 
CULTURAL CHARACTERS 
The organism grows well on potato agar with 1 or 2 per cent 
dextrose and no peptone, and this medium has been generally used. 
Equally good growth occurs on lima-bean agar without dextrose. 
Unless otherwise specified, the cultures were incubated at room 
temperature. The reaction of the media as expressed in Fuller’s 
scale was adjusted by titration, using as the neutral point the first 
permanent but faint pink color with phenolphthalein. Inoculations 
were made from water suspensions unless otherwise stated. Cultures 
of Bacillus coli and Bacterium glycineum Coerper were carried in 
parallel series in part of the tests. 
Agar poured plates. —On + 10 beef-peptone agar, colonies appeared in 24 
hours; and in 56 hours surface colonies were 2 mm. in diameter, and round, 
raised, glistening, and grayish white. Submerged colonies were smaller and 
lens shaped. In six days surface colonies were round with an entire margin, 
raised, and smooth, with a finely granular internal structure showing faint 
concentric markings (pi. 4, A). The color was grayish white in reflected light 
and slightly fluorescent in transmitted light. 
Surface colonies on potato-dextrose agar incubated four days at 27° C., were 
3 to 4 mm. in diameter, and in one week were 5 to 7 mm. in diameter. The 
colonies were round, and the margin entire (pi. 4, A); the surface was smooth or 
concentrically ridged; and the elevation varied from raised to pulvinate, with 
the central portion often higher, making the colony umbonate. The colonies 
had a finely granular appearance, with a more or less concentric pattern, as 
