226 
Journal of Agricultural Research 
Vol. XXVII, No. 4 
often found only on the middle area of the leaf. As seen in fresh 
material, these spots are translucent and watersoaked. In reflected 
light the color is a very dark green; in transmitted light it is a bright 
green. The translucency of the spots is permanent, but when old and 
dry the colors are various shades of brown. 
Considerable quantities of a bacterial exudate flow from the affected 
tissues. In quiet, dry air this exudate forms slender, twisted white 
columns 2 to 10 mm. long. Under moist conditions it forms a viscid film 
over the leaf. When dry it may be a thin, brittle layer or it may occur in 
the form of numerous small droplets. Wind-blown soil, tiny insects, 
and various small particles become embedded in this exudate, often in 
sufficient quantities to cover the leaf surface. The exudate seems to be 
composed entirely of bacteria; it dissolves readily in water and doubtless 
is a factor in the dissemination of the disease. 
The name Bacterium gummisudans proposed for the causal organism of 
this disease, was suggested by the copious exudate from the lesions. 
ISOLATION AND REINFECTION 
Yellow, viscid bacteria were repeatedly and easily isolated from the 
lesions and from the exudate, and numerous inoculation experiments have 
proved these bacteria to be the cause of the disease. 
From lesions produced by pure culture inoculations the organism was 
reisolated on agar-poured plates and with subcultures from single colonies 
typical reinfections were obtained. Repeated experiments in inoculating, 
reisolating, and reinfecting leave no doubt either as to the cause of the 
disease or as to the general character of the lesions. 
Young plants grown from cormels were readily infected. Older plants 
were more resistant. Of six varieties of mature plants used for inocula¬ 
tion experiments, Schwaben was the only one that became generally 
infected; Mrs. Francis King was very slightly infected. On Mrs. Frank 
Pendleton no infection occurred. These inoculation results agree with 
the field observations in regard to relative susceptibility of young and 
mature plants and of varieties: 
Iris, hyacinth, and barley were inoculated but no infections resulted. 
MORPHOLOGY 
The organism is a short, actively motile rod, occurring singly and in 
pairs in the host and in most culture media. In beef bouillon it forms 
long chains. It measures when stained with carbol fuchsin 1 to 2 .Six by 
0.6 to o.Sfx ; no spores have been seen. Capsules are formed on beef 
peptone agar and on potato dextrose agar. The single polar flagellum is 
3 to 9 fx long. The flagella were demonstrated by the use of Casares-Gil’s 
staining method. It is Gram-negative and not acid-fast. 
CULTURAL CHARACTERS 
On peptone beef 2 agar the colonies are pale yellow (amber yellow 3 ), 
circular, transparent; the surface is smooth and the interior has con¬ 
centric striations (PI. 2, F). With age the growth becomes less trans¬ 
parent and the striae disappear. Buried colonies are oval to spindle-shape 
and have definite margins. 
2 All the beef media used in this study were made from fresh beef infusion with addition of i per cent 
Difco peptone corrected to +14 to 4-18 Fuller’s scale (Ph 6.8 to 6.4). 
3 Ridgway, Robert. color standards and color nomenclature. 43 p., 53 col. pi. Washington, 
D. C. 1912. 
