FLORIDA STATE HORTICULTURAL SOCIETY 
83 
According to the observations of Dr. 
Berger and M,r. Frank Stirling, aside 
from the grapefruit and trifoliata, the 
other citrus varieties are susceptible to the 
disease about in the order named: Key 
Lime, Navel Orange, Sweet Orange, Sat- 
suma, Tangerine, Mandarin, King Or¬ 
ange and Lemon. 
cause 
(Note: A few days after this paper was read, 
new facts regarding the cause of citrus canker 
came to light, and in order to avoid confusion 
and bring the information on this disease up to 
date, it seems advisable to omit that part of the 
original discussion relating to the cause and sub¬ 
stitute instead our more recent information on 
this subject.) 
Recent experiments of my own and the 
work of Miss Hasse, of the Bureau of 
Plant Industry, show that citrus canker is 
caused by a species of bacteria rather than 
by a fungus. 
In the paper as read before the Society 
the writer gave as the cause of this dis¬ 
ease a species of fungus which was classed 
as one of the Phyllostictas. Some infec¬ 
tion experiments of my own in which 
typical canker spots were produced from a 
single spore colony of the fungus (Fla. 
Expt. Sta. Bui. 124, p. 39), and the work 
of Dr. F. A. Wolf and A. B. Massey of 
Alabama (Ala. Agrl. Expt. Sta. Cir. 27, 
pp. 99 and 100), formed the basis for this 
opinion. The constant association of this 
fungus with canker infections, collected 
from widely separated areas, has also add¬ 
ed weight to the fungus theory. 
I have pointed out, however, that most 
of my infection experiments have given 
negative results and in only a few cases 
have I been able to produce typical canker 
spot with cultures of this fungus. This 
difficulty finally led me to suspect that bac¬ 
teria were probably concerned in the de¬ 
velopment of the disease. Some experi¬ 
ments were made to determine this a few 
days previous to the meeting of the Horti¬ 
cultural Society in Tampa. Some small 
citrus trees in pots were inoculated with 
spores of the fungus, a combination of 
the fungus and bacteria isolated from a 
canker spot, and the bacteria alone. The 
trees thus treated were examined on Sat¬ 
urday following the Tampa meeting, and 
the results were convincing that bacteria 
were primarily the cause of the dis¬ 
ease. Where the bacteria were used alone 
and in combination with the fungus, typi¬ 
cal canker spots were developing. The 
following Monday information was re¬ 
ceived from the United States Depart¬ 
ment of Agriculture to the effect that 
Miss Clara H. Hasse had some time prev¬ 
iously discovered that citrus canker was 
caused by a species of bacteria which she 
had described and named as Pseudomonas 
citri. A short account of the work and a 
description of the organism was published 
in the April number of the Journal of Ag¬ 
ricultural Research. 
Infection experiments are being con¬ 
tinued with this organism and in every 
case so far young citrus foliage that has 
been inoculated with cultures of the bac¬ 
teria have developed canker infections. 
The work has not progressed far enough 
at present to permit of any detailed report. 
I regret that my discovery of the cause 
was not made sooner, however, this new 
information does not change the canker 
situation in the least. The fact that citrus 
canker is caused by a species of bacteria 
rather than by a fungus does not make 
