664 Journal of Agricultural Research voi. xv.no. la 



of this species were found by Prof. G. W. Groff and the writer near the 

 summits of mountains in Kwangtung Province at an altitude of about 

 1,500 feet. These mountains are heavily eroded and peculiar in having 

 their sides barren and almost entirely free from growth. Plants of F. 

 hindsii at the tops of these mountains were therefore very much isolated 

 from commercial Citrus plantings and other sources of canker infection ; 

 nevertheless, in almost all cases the species was heavily infected with 

 Citrus-canker. The writer later found plants of the same species upon 

 Victoria Peak, Hongkong, a mountain of very similar type. It is pos- 

 sible that further facts may show that this plant is an original wild 

 host from which Citrus-canker has spread to cultivated species. 



Chaetospermum glutinosa occurs both naturally and cultivated at 

 Lamao, and naturally occurring cankers are abundant upon such plants. 

 The susceptibility of C. glutinosa to canker is easily greater than that of 

 the sweet orange (Citrus sinensis) in the Philippines. 



Glycosmis pentaphylla occurs naturally in Kwangtung Province, China, 

 in places where infection from Citrus-canker would be easily possible. 

 No naturally occurring cankers were observed. 



Of the positive results obtained in the foregoing tabulated species, 

 Pseudomonas citri has been reisolated from Claucena lansium, Feronia 

 limonia, Feroniella lucida, Chaetospermum glutinosa, Hesperethusa crenu- 

 lata, Paramignya longipedunculata, Citropsis schweinfurthii, A talantia cit- 

 rioides, Fortunella hindsii, Microcitrus australasica, M. australis, Toddalia 

 asiatica, and Evodia ridleyei. Such isolations have been reinoculated on 

 foliage of Citrus grandis, and have given positive results in each case. 

 In those positive results not listed as having the organism reisolated the 

 material was collected and dried in the field, where laboratory facilities 

 were not available. 



The statements made above as to immunity, since they are based on 

 lack of infection after inoculation with a dense infusion of the causal 

 organism under the most favorable conditions for infection, are probably 

 more substantial than claims made for absence of infection under natural 

 conditions. 



The most noteworthy feature of the inoculations is the susceptibility 

 of such very distant relatives as Evodia ridleyei, E. latijolia, and Meli- 

 cope triphylla. In these cases the cankers are by no means weakly pro- 

 duced, but form quickly, with a decided swelling of the tissue, which later 

 erupts as on species of Citrus. On E. ridleyei the results were evident in 

 two weeks. Pseudomonas citri, therefore, is not closely limited to Citrus 

 spp., but has a very wide range of host plants within the family Rutaceae. 



Severinia huxifolia, Aegle marmelos, and Balsamocitrus gabonensis 

 produce no reaction whatever when inoculated with Pseudomonas citri. 

 It is believed that these species may be safely called immune to Citrus- 

 canker; this is especially noteworthy, since they are all close relatives of 

 the genus Citrus. 



