220 



Journal of Agricultural Research 



Vol. XIX, No. s 



as was shown by Petri dish platings soon after the series was begun, 

 and the results from them are not included in the tabulation. The per- 

 centages in Table XI are based on infection in i ,500 punctures. 



Table XI. — Percentages of infection on grapefruit leaves inoculated with graded dilu- 

 tions of distilled water, autoclaved spring water, and unautoclaved spring water at 

 various intervals after the water had been inoculated with P. citri 



Two other series confirmed the very rapid decline noted above in either 

 distilled or ordinary surface water when it is nonsterile. Contrasted 

 with this is the long persistence of moderately reduced numbers of the 

 organism in the sterilized spring water. 



The question is sharply raised, does autoclaving promote the per- 

 sistence of P. citri in soil or water by destroying something that is dele- 

 terious or by producing something that is favorable? Autoclaving, in 

 general, has its greatest effect in destroying the organic fauna and flora 

 of the medium, and a subsidiary one in modifying the nutritive materials 

 contained in it. The supposition that starvation may be the cause of 

 the normal decline and that autoclaving the soil supplies enough avail- 

 able nutriment for a greatly prolonged persistence does not seem reason- 

 able because of the disproportion between the changes that could possibly 

 be brought about by autoclaving and the effects observed on P. citri 

 persistence. Furthermore, this supposition of starvation is not adequate 

 to explain the extinction of P. citri in air-dry soil when moistened. 



INHIBITORS 



The deleterious effects of organisms on the development of P. citri 

 is frequently observed in poured plates when fungus or bacterial con- 

 taminators entirely inhibit the development of P. citri for considerable 

 distances from their limits of growth. The behavior of some of these 

 inhibitors has been made the subject of special preliminary study. 



A series of plates was prepared September 13, 191 9, from beef agar 

 rather heavily and uniformly inoculated with P. citri. When hard, 

 they were inoculated in addition with a bacterium, designated inhibitor 

 A, previously obtained from a chance contamination on a poured plate. 

 On some plates two streaks of the inhibitor were made at right angles 



