2l6 



Journal of A gricultural Research 



Vol. XiX, No. 5 



Heavy initial inoculation, frequent samplings over a long period, and 

 inoculation at each sampling of 40 or 30 grapefruit leaves with 100 punc- 

 tures each for the respective series render the results in these series 

 especially noteworthy. In the moist series, after the fourth day, one 

 notes a general equality of percentages on diagonals extending downward 

 and to the left from any of the 1/1,000 figures. For example, the 1/1,000 

 dilution on the fourth day, the i/ioo on the seventh, the i/io on the 

 ninth, and the i/i on the eleventh are approximately the same, indicat- 

 ing a nine-tenths loss in actual numbers in the soil for each sampling 

 interval as compared with the preceding one; and this seems to hold 

 true until the fortieth day. It may be explained that the moist series 

 suffered much from the dropping of leaves heavily infected from the 

 early samplings, and the resulting figures are somewhat erratic. 



In the dry series there is a decided drop following the initial drying 

 immediately after inoculation. Then follows a slow decline followed by 

 an inexplicable increase between the tenth and thirty-fourth days. 

 Afterwards there is an extremely gradual decline, if any, extending to the 

 one hundred and sixty-sixth day. 



On October 27, 1919, the one hundred and twelfth day of the test, a por- 

 tion of the soil was removed from each of the three dry pots and moistened 

 with sterile distilled water. The following tabulation shows the results 

 of inoculation tests made from these moistened lots in comparison with 

 the original dry soil. Two thousand punctures were inoculated from 

 each lot of soil, making 6,000 for each test of moistened or of dry soil. 

 The figures are total infections from 6,000 punctures. 



Dry soil 



Moistened soil. 



Date of sampling. 



Oct. 29. 



Oct. 31. 



Nov. 3. 



Nov. 5. 



Nov. 7. Nov. 10. 



Nov. 17. 



The application of sterile distilled water seemingly resulted in prompt 

 and complete extinction of P. citri in this dry soil which had constantly 

 shown the presence of at least small numbers of the organism during 

 almost four months. A repetition of the test, begun November 14, 191 9, 

 confirms these results. 



That this extinction was not due to any toxic property peculiar to the 

 distilled water was shown by a second test begun December 13, 191 9, in 

 which spring water and deep well water were used for wetting the soil. 

 Tests on the third and seventh days were negative for all lots of moist- 

 ened soil, while the dry soil continued to show the usual trace of P. citri. 



That rate of drying would have an influence on the residuum of P. citri 

 is to be expected and probably accounts for some of the irregularities 



