junei.i92o Behavior of the Citrus-Canker Organism in the Soil 195 



was one positive result and on the second day following the rain there 

 was a positive result. Thereafter on the third, fourth, fifth, seventh, 

 and ninth days the results were entirely negative. On these days a total 

 of 125 leaves, or 5,000 punctures were inoculated with the soil infusion, 

 and all remained negative. 



The conclusion is reached, then, that although the canker organism 

 was present immediately following the rain, in this case the citrus-canker 

 organism has died out in the orchard soil. 



REPETITION OF EXPERIMENTS I AND II 



The field data have been very extensive in support of the theory that 

 the canker bacteria can exist and multiply in the soil. Since the idea 

 has been so firmly held by growers and horticulturists that the canker 

 organism does live in the soil, and because the data presented in the two 

 preceding experiments indicate the contrary to be the case, both these 

 experiments were repeated. 



Experiment I was repeated, and the original results were entirely cor- 

 roborated. It was found that P. citri was abundant in the unsterilized 

 soil tubes during the first, second, and third days; during the fourth, 

 fifth, seventh, and ninth days the inoculations were but very slightly 

 positive; on the fourteenth day the organism showed three positive 

 results from a total of 4,000 punctures. In the sterilized soil tubes P. 

 citri gave almost uniformly 100 per cent results up to and including the 

 fourteenth day. 



Experiment II was carried through three times. The first trial has 

 been reported here in detail. For the second and third trials the same 

 methods were used. In a second trial the water dripping from the foli- 

 age of an infected grapefruit tree was shown to contain P. citri in a large 

 percentage of cases. The soil beneath the tree, immediately following 

 the rain, also gave a large number of positive results. On the second day 

 after the rain and thereafter for four days inoculations from the soil 

 beneath the same tree gave entirely negative results on the pummelo 

 leaves. In a third trial no tests were made with the rain water on the 

 leaves, but immediately following the rain a large number of positive 

 results were obtained on pummelo leaves from inoculations with the 

 soil infusion from beneath the cankered foliage. On the first day after 

 the rain a few positive results were obtained from the soil infusions, but 

 on the second day none of the inoculations resulted positively. On the 

 third and eighth days there were again a few positive results, but on the 

 tenth day 2,000 inoculations made from the soil upon the pummelo 

 leaves remained entirely negative. These second and third trials en- 

 tirely corroborate the experiments reported above and indicate that the 

 citrus canker organism is entirely killed in orchard soils. 



The tests of orchard soil were carried on at different seasons of the year 

 and are representative of the conditions in the soil in very different 



