junei,i92o Behavior of the Citrus-Canker Organism in the Soil 203 



and there is no reason to base a supposition for unusual bacterial activity 

 on such grounds. The soil used in the experiments was taken from 

 directly beneath trees of the Ellen grapefruit variety and was plowed, 

 cultivated, and hoed according to usual orchard practices. The treat- 

 ment of the soil differed very little from that usually practiced in the 

 United States. 



APPLICATION OF RESULTS 



The writer would prefer that any applications of these findings be made 

 by the field men, who are in the best position to judge the merits of 

 different methods in eradication work. The following suggestion might 

 be made, however, from a theoretical viewpoint. 



It is frequently stated that canker is carried from orchard to orchard 

 upon muddy feet or in the earth upon farm implements. These state- 

 ments appear to be based upon a wrong conception of the character of 

 the canker organism, and it would seem probable that the disease bacteria 

 are carried upon dry portions of clothing and implements rather than in 

 the earth. These experiments should therefore serve not to decrease 

 the vigilance of quarantine measures but to increase the precautions to 

 eliminate all sources for reinfection and dissemination of canker; for 

 inasmuch as these experiments indicate that the canker organism does 

 not live in the soil, field data which seem to indicate that P. citri is a soil 

 inhabitant must be explained as indications of a source of reinfection 

 overlooked or of a careless transfer of the organisms by farm animals or 

 man. 



SOME POSSIBLE SOURCES FOR REINFECTION BY THE CANKER ORGANISM 



It has been demonstrated by Peltier and Neal ^ that the canker organ- 

 ism may overwinter in the bark tissue of citrus trees. The following 

 observations may supplement their findings as to the means of over- 

 wintering or survival. 



In the Philippine Islands lesions very much resembling those of citrus- 

 canker were observed upon the mature wood of grapefruit trees {Citrus 

 maxima) and lime (C. auraniijolia). These lesions were of a slightly 

 lighter brown color than the normal bark and consisted of eruptions of 

 tissue very similar to cankers upon leaves. Examinations of frozen 

 sections of such eruptions revealed the typical structure of citrus-canker 

 and the masses of bacteria distributed as in leaf cankers. P. citri was 

 subsequently isolated from these lesions. Photographs (PI. 36) show 

 these mature wood cankers better than a description. The mature 

 wood cankers were also observed upon navel orange trees (C sinensis) 

 in orchards in Japan. 



Close examination has revealed that these mature wood cankers are 

 by no means uncommon on lime, grapefruit, and sweet orange trees; 



* Peltier, George L-, and Nbal, David C. overwintering of the otrus-canker organism in thb 

 BARK TISSUE OF HARDY CITRUS HYBRIDS. In Jour. Agr. Research, v. 14, no. 11, p. 523-524, pi. 58. 1918. 



