338 
Journal of Agricultural Research 
Vol. XIV, No. 9 
The results obtained from two sets of inoculation experiments in the 
greenhouse for the past five months have been of such a nature that their 
publication at this time is deemed advisable. It must be kept in mind 
that the results here reported are only of a relative nature, and in no 
case must they be considered absolute. This is especially true of those 
plants which are reported resistant. Of course, in the further search for 
varieties which are resistant to canker, the plants which showed marked 
susceptibility in the greenhouse experiments will be discarded. 
EXPERIMENTAL METHODS 
Organism used. —The organism (Pseudomonas citri Hasse) used in the 
inoculation experiments was isolated by Mr. D. C. Neal, by the ordinary 
dilution methods directly from soil taken under an infected grapefruit 
(Citrus* grandis) near Fairhope, Ala., on July 20, 1917. Preliminary 
inoculations with this strain on grapefruit and Satsuma orange ( Citrus 
nobilis var. unshiu) in the greenhouse proved that it was exceedingly 
virulent. 
Type of plants used. —Practically all of the plants used in the inocu¬ 
lation experiments were grown either from seeds or cuttings in the green¬ 
houses at Washington, D. C. A few plants were included which had 
been budded on Poncirus trifoliata Raf., obtained from nurseries in 
Alabama. The size of the plants varied from 6 inches to 4 feet in height, 
and from those having a single stem to the large plants which had been 
cut back, with numerous shoots. The first lot of plants was received 
from Washington, D. C., on July 21, 1917, while the second shipment 
arrived on October 1, 1917. The plants were either cut back or were 
in a dormant condition when received; but by the time the first inocula¬ 
tion experiment was started, the majority were in excellent shape for 
infection. In discussing the results of the experiments the Crop Physi¬ 
ology and Breeding Investigations' (CPB) numbers used by Mr. Swingle 
are given so that the origin of the plants can be traced at any time 
by consulting his records. 
Method of inoculation. —As the plants varied in height, three sizes 
of inoculation cases were used. Care was taken in mixing the plants, 
so that all types were represented in each case. Just before setting the 
plants in the cases six punctures were made with a sterile needle on a 
mature leaf and an old leaf of each plant. The maturity of a leaf was 
judged by the size, condition, and to some extent by the number, size 
and pore length of the stomata. In a preliminary study it was possible 
to distinguish the different ages of the leaves by the methods used by 
Pool and McKay (16) 1 in their study of the species of Cercospora on beet. 
The results of the inoculation experiments were such that, unless stated 
in the discussion, no mention will be made of the infections occurring at 
the punctures. 
1 Reference is made by number (italic) to “Literature cited,” p. 356-357. 
