340 Journal of Agricultural Research voi. xix.no. s 



same manner — that is, infusions of 48-hour-old cultures of Psendomonas 

 citri Hasse in beef bouillon were sprayed on the foliage of the plants 

 by means of an atomizer. In no cases were punctures made, but wounds 

 and scratches were present on some of the leaves. The plants all 

 received identical treatments and were under approximately the same 

 conditions. 



The plants in experiment I were inoculated August 27 and September 

 12, 1 91 7, and those in experiment II were inoculated October 23 and 

 November 9. On March 23, 1918, the plants were all trimmed or cut 

 back to force new growth, and some new numbers were placed in the 

 screen cases together with the others. All of these were then inoculated 

 in the usual manner. On the same date, the plants in experiment III 

 were inoculated and have remained in the glass cases. Thus, after 

 initial infection was obtained, natural inoculations of the remainder of 

 the plants were counted on entirely. Therefore, natural infection took 

 place on the greater part of the plants reported on in the following pages, 

 especially on the more resistant plants. 



In the isolation field, plantings were made in 1917, 1918, and 191 9. 

 Some of the nonhardy relatives and Citrus fruits were killed by hard 

 winters of 191 7-1 8 and 191 8-19, but the majority of the plants sur- 

 vived. Inoculations in the field were started in September, 191 7, by 

 Mr. D. C. Neal and were later continued by Mr. J. Matz up to November 

 I, 1918, when the plants were banked for the winter. During the 1919 

 season the inoculations and observations in the field were made by the 

 junior author.^ Some of the plants were inoculated only once or twice, 

 while others were sprayed with the inoculum regularly every week 

 throughout the season. The time chosen for inoculation varied, but 

 as a rule the late afternoon was chosen. A large number of natural 

 infections took place after canker had been established on some of the 

 plants. 



The seasons of 191 7 and 191 8 were normal so far as climatic conditions 

 were concerned. However, during the 191 9 season the temperature was 

 high, and together v.dth an excessive and frequent rainfall it afforded not 

 only ideal conditions for plant growth but also for the most rapid infection 

 and development of canker. 



Unless otherwise stated, all the plants reported on were in a good 

 growing condition, and the organism was reisolated from the doubtful 

 canker spots, especially in the case of the wild relatives. It must also 

 be borne in mind that tlie plants used were for the most part small 

 seedlings or nursery stock. Thus, the size of the plants and the condi- 

 tions under which the inoculations were carried out made them more 

 susceptible to canker. Plants reported here as susceptible would proba- 

 bly show more resistance under orchard conditions. No doubt maxi- 

 mum susceptibility was obtained with the plants experimented upon. 



' The senior author is solely responsible for all conclusions drawn from the results of the three years' work. 



