June X, 1920 



Decline of Pseudomonas citri in the Soil 



211 



P. citri evidently decreased very rapidly in all these soils and appar- 

 ently reached the vanishing point in all in less than 14 days. The rate 

 of decrease was most rapid for the clay subsoil, slightly less so for the 

 leaf mold, and distinctly slower for the compost and garden soil. 



A second test was begun September 7, 191 8, with new lots of soil from 

 the same sources with the addition of well-washed sand from a creek bed, 

 and a mixture of equal parts of the leaf mold and garden soil used in the 

 earlier experiment. The initial inoculation was about 50 per cent heav- 

 ier than in the preceding series. In order of rapidity of decrease clay 

 subsoil proved again to be first, followed by leaf mold, sand, compost, 

 garden soil, and mixture of leaf mold and compost. At the termination 

 of this test, 14 days after inoculation, the red day was the only one giving 

 negative results; and the percentages for the leaf mold, compost, and 

 garden soil were approximately those given for the ninth day in Table I. 

 This longer persistence in the second test may reasonably be attributed 

 to the higher initial inoculation of the soil. 



In other experiments the following citrus soils from Florida were 

 used: (i) from Orlando, intermediate between high and low pine soil 

 types, unusually rich in humus; (2) similar to (i) but naturally poor; 

 (3) similar to (2) but from a poorly drained spot; (4) from Bradentown, 

 low pine land of low fertility; (5) from Bradentown, typical muck, ex- 

 tremely rich in humus; (6) from Winter Park, high hammock type; 

 (7) from Winter Park, low hammock type. The samples, as a rule, 

 reached the laboratory and were set up before becoming dry. The usual 

 dilutions to 1/1,000 were run, but for brevity the percentages from the 

 i/i dilution only are given in Table III. At the higher dilutions the 

 commencement of decline was evident at the second sampling for all 

 types, whereas this decline is not evident from the i/i figures of the table 

 until the fifth or sixth day. The tests were made during September and 

 October, 19 18, in three distinct series, as indicated in the table. The second 

 and third were conducted by Miss Clara H. Hasse, of this office, through 

 whose courtesy the results have been furnished for this publication. The 

 percentages are based on infection development from 600 punctures. 



