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



raised, and corky, resembling those found on Citrus. The other three 

 species of kumquats tested are equally resistant. While infection has 

 been more or less general in the greenhouse on the young foliage the 

 spots with but few exceptions have remained unruptured. 



Thus, outside the subtribe Citrinae, only two susceptible plants, Hes- 

 perthusa crenulata and Chaetospermum glutinosum, have been found under 

 greenhouse conditions. The rest of the plants which were successfully 

 inoculated all produced nontypical, unruptured spots at wounds. To 

 this group can be added Citropsis Schweinfurthii. The plants reported 

 free from canker will probably remain immune, while other plants not 

 tested may prove susceptible when inoculated. The remaining plants 

 in the subtribe Citrinae have all been successfully inoculated. 



In the field successful inoculation both natural and artificial have been 

 produced on Hesperthusa crenulata, Poncirus trifoliata, Fortunella Hindsii, 

 F. margarita, F. japonica, Microcitrus australasica, and M. austrahs. 

 Of these P. trifoliata and M. australis are very susceptible. No doubt 

 under favorable conditions Atalantia citrioides, A. ceylonica, Eremocitrus 

 glauca, and Chaetospermum glutinosum can be successfully inoculated in 

 the field. However, none of them will prove as susceptible as P. tri- 

 foliata. 



Thus, only the relatives most susceptible under greenhouse conditions 

 have been successfully inoculated in the field. So far as the menace of 

 citrus-canker to the Citrus industry in the United States is concerned, 

 with the exception of Poncirus trifoliata, none of the relatives, native or 

 introduced, discussed above are susceptible enough to warrant further 

 attention. 



The index of susceptibility to citrus-canker of these plants should be 

 based not on the ability to successfully produce canker infections through 

 needle pricks or wounds, under abnormal conditions, but rather on the 

 ability of the organism to gain entrance into the tissues through natural 

 openings of the leaves in the absence of both artificial and natural wounds. 

 Therefore, the senior author believes that even though he has been able 

 to inoculate a large number of the wild relatives the results have no bear- 

 ing on the eradication program. It is purely of scientific interest to 

 know that P. citri is not limited to the genus Citrus but can produce, 

 under certain conditions, infections on a wide range of plants in the family 

 Rutaceae to which Citrus belongs. 



The senior author has devoted considerable attention to a study of the 

 various types of spots produced on the various hosts, hoping to be able 

 to correlate the type of spot with resistance. In brief, the spots as 

 observ^ed on the relatives can be classed as follows: Small, slow growing, 

 nontypical, unruptured spots (PI. 57) occurring only at wounds on 

 rutaceous plants; same type of spots, but occurring on the leaves in the 

 absence of wounds (on Feronia limonia); more typical spots (PI. 60, A) 

 which are unruptured except at wounds (on Fortunella margarita); and 

 typical, ruptured, corky spots (PI. 63, D) (on Poncirus trifoliata.) 



