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



Six days after the inoculation with the heavy infusion no indications of 

 the organism could be obtained from this soil. As a control upon the 

 conditions a similar box of soil, alike in every detail except that it had 

 been autoclaved, was inoculated; it showed the continuance of the canker 

 bacteria throughout 14 days, and the bacteria were apparently as numer- 

 ous on the fourteenth day as on the first. 



These experimental results, as well as those with the tubed soils, indi- 

 cate that the canker organism does not increase and multiply or live 

 even a passive existence in the normal soil but is quickly killed out. 

 Inasmuch, however, as it will live in soil from which all other organisms 

 are excluded, there is indication that in unsterilized soil the activities of 

 the normal soil organisms are antagonistic to the existence of P. citri. 



The follov/ing results obtained by a different experimental procedure 

 still further corroborate the previous conclusions. 



EXPERIMENT IV 



This experiment was conducted to show the persistence or absence of 

 the canker bacteria by growing susceptible plants in inoculated soils. 



Ten bamboo pots were autoclaved and subsequently filled with soil 

 twice autoclaved. These soil pots were then heavily inoculated with a 

 dense infusion of P. ciiri in sterile water. On the same day 30 bamboo 

 pots filled with unsterilized soil were inoculated with the canker organism 

 from similar infusions. 



Pots I to 5 of sterilized, inoculated soil were immediately planted 

 each with 10 seeds from Citrus trijoliata fruits; pots 11 to 20 of unsteri- 

 lized, inoculated soil were also immediately planted each with 10 seeds of 

 C. trijoliata. After an interval of 5 days 10 miore pots of unsterilized, 

 inoculated soil were planted each with 10 seeds; and after an interval 

 of 10 days 10 pots of unsterilized soil and 5 more pots of sterilized soil 

 were planted, each pot with 10 C. trijoliata seeds. 



It was the intention, of course, that the Citrus trijoliata seedlings 

 resulting would be very susceptible and in growing through the inocu- 

 lated soil would become infected if the canker organism still remained 

 alive within the soil. 



Running parallel with these series of inoculated soil pots, a series of 

 orchard soil pots was operated as follows: Ten pots were filled with soil 

 taken from beneath a heavily infected grapefruit tree, immediately 

 following a rain, and each pot was planted with Citrus trijoliata seeds. 

 The tree was cut down and all sources of infection were removed from 

 the soil; then 10 days later 10 more pots were filled with the same soil 

 and similarly planted. 



All pots, those containing orchard soil naturally infected and those 

 artificially inoculated, were covered with cheesecloth after planting to 

 prevent the ingress and egress of insects which might spread infection. 



