524 
Journal of Agricultural Research 
Vol. XIV, No. II 
Notwithstanding the fact that all the plants were carefully observed 
at intervals throughout the winter, no infection was found on the hybrids, 
although these were in a thrifty condition, with an abundance of healthy 
foliage. 
On April 2, 1918, positive evidence of Citrus-canker infection was 
observed on the Rusk and Savage citranges, as well as on the citrandarin. 
The plants of P. trifoliata (PI. 58, B) that were inoculated at the same 
time (September 16, 1917) also revealed new infections. Unfortunately 
the grapefruit and Satsuma plants were killed by the low temperatures 
prevailing during the winter months, and no further data could be 
obtained here. The hybrid plants were heavily infected, the infection 
in each case being confined to the main stem and branches (PI. 58, 
A, C, D). The infection appeared simultaneously and extensively on all 
the twigs, branches, and main stems of the plants. Although the foliage 
was very healthy and apparently active and had been so throughout the 
winter, no sign of infection was observed on the leaves. 
Cankered twigs from the Rusk and Savage citranges, the citrandarin, 
and C. trifoliata were collected and taken to the laboratory to ascertain 
whether the organism was viable and could be recovered in culture. 
Within four days good colonies of the organism appeared on the plates, 
which left no question of their viability. 
From the data at hand it would appear that the Citrus-canker organ¬ 
ism is able to withstand the winter within the outer-bark tissues of the 
host. Wolf 1 states that the lenticels probably serve as portals of 
entrance for the organism into the stems, and from the results it would 
appear that this view is entirely possible. The organism probably 
gains entrance into the outer-bark tissue through the lenticels and 
remains dormant through the winter months. On the return of more 
favorable conditions of temperature, humidity, and rapid growth of the 
plant, the canker organism becomes active. 
The weather records in this vicinity during the fall and winter of 
1917-18 reveal a minimum temperature of 15.5 0 F. It would seem, 
therefore, that the bacteria which gained entrance into the outer-bark 
tissues, probably through the lenticels, at the time of inoculations, Sep¬ 
tember 16, 1917, were offered sufficient protection to withstand the above 
temperature, whereas the foliage infections were completely killed or 
their virulency lowered to such an extent that infection was not possible. 
From the fact that the Citrus-canker organism is able to withstand 
such a low temperature and remain in a dormant condition for 6 % months 
in the outer-bark tissues of the twigs and branches, extreme care and 
caution must be exercised in the use of Citrus plants from canker-infected 
regions in the selection of budwood from nurseries and orchards in which 
canker has been found within a year, in the length of the quarantine 
period, and in the complete eradication of Citrus-canker from nurseries 
and orchards, especially in plantings of P. trifoliata . 
1 Wow, F. A. citrus-canker. In Jour. Agr., Research, v. 6, no. a, p. 79- 1916. 
