Feb. 3, 1923 
Bacterial Leaf spot of Geranium 
371 
MORPHOLOGY OF THE ORGANISM 
The organism was studied in the cells of the spots on the leaves which 
had been sectioned and stained with carbol fuchsin and in 2-day-old 
beef agar cultures stained with carbol fuchsin. It is a short rod with 
rounded ends; stained in diseased material it is 0.62 n to 1.46 ju long and 
0.61 jx to 0.83 }x wide. In the agar cultures the size is 0.62 to 1.25 n 
long and 0.41 ix to 1.04 /x wide. In cultures the rods hang together in 
chains of 2 to 16 elements, but mostly 6 to 8. Capsules were demonstrated 
in 2-day-old agar cultures stained with Ribbert’s capsule stain and also 
with carbol fuchsin. 
Flagella were stained with Casares-Gil’s flagella stain. There is one 
flagellum at a pole, rarely one at each pole. One case was observed of 
a branched flagellum at a single pole. No spores were demonstrated in 
a culture of any age nor were any involution forms seen. The organism 
is not acid fast nor does it stain by Gram’s method but is stained readily 
with ordinary basic aniline stains. 
The morphological differences between the two organisms are slight. 
The size of the Lewis organism is 1.2 to 1.8 ju by 0.6 to 0.8 n, with rare 
involution forms. No spores or capsules are demonstrated. It is Gram 
negative, not acid fast, and bears 1 to 3 polar flagella at one pole only. 
NATURAL INFECTION AND CONTROL 
The disease under the writer’s observations is one that occurs through¬ 
out the Eastern States in greenhouses and attacks the plants usually 
when they are rooted cuttings and growth is being forced. We have 
never noticed the disease on old, slow-growing plants except in a few 
cases when the plant had been cured of the disease and then the spots 
were few and on leaves that had held over from the early attack. When 
the disease occurs out of doors, as it sometimes does, it is due to crowd¬ 
ing or to unfavorable weather conditions acting on susceptible varieties. 
The occurrence of the disease on the grounds of the United States 
Department of Agriculture was mentioned in the early part of this 
paper. It is probable that the disease began in the greenhouse un¬ 
observed and continued when the plants were set out in the beds, hot 
weather and moist conditions favoring a rapid development of the 
disease. It has not occurred in the grounds for the last 10 years, the 
very susceptible varieties having been discarded. 
There has never been any insect present on any of the diseased material 
received from the various sources. Occasionally geranium leaves are 
received which are infested with red spider (Tetranychus telarius L.)> 
but the spotting due to this mite is of a different type. 
From all the evidence gathered the organism seems to be one harbored 
in the soil. The disease is not a serious one unless the physical condition 
of the plant is weakened by too rapid growth and too moist or too warm 
an atmosphere with little chance of air circulating between plants, and 
last, but not least, too little care in watering. 
Experiments leading to the control of the disease could not be under¬ 
taken in the greenhouses where the disease occurred because of distance. 
Control work, however, was attempted with our own plants on which 
the disease had been produced. The spotted leaves were picked off, 
the plants separated from each other in order to give them light and 
