214 



Journal of Agricultural Research 



Vol. XIX, Xo. s 



and too little attention was given to watering the pots regularly during the 

 latter part of the experiment. But the outside pots retained moisture 

 much better than those inside, and any difference would have been 

 against longer persistence in them. 



INFLUENCE OF SOIL MOISTURE ON PERSISTENCE 

 A test was begun September 2, 1918, using ordinary potting soil. 

 Inoculation was with a mixture of beef bouillon and potato cylinder 

 cultures. One set of duplicate pots was kept near the saturation point 

 by watering thoroughly every other day. A second lot was restored at 

 each watering to the halfway point between saturation and the original 

 air-dry condition of the soil. The third set was left unwatered. The 

 percentages in Table VI are based on 600 inoculated punctures. 



TabliS VI. — Percentages of infection on grapefruit leaves inoculated with graded dilu- 

 tions of soil solution at various intervals after the soil had been inoculated with P. citri 

 and had been held at three moisture contents 



The foregoing test shows no very pronounced or definite differences in 

 rate of decrease. The slight differences tend toward lag with decrease 

 of moisture, the moderately watered soil showing possibly less rapid 

 decline than the saturated, and the air-dry soil showing still greater 

 retardation. 



Further tests of moderately wet soil as compared with dry were made 

 at different times vv'ith three lots of Florida soil and are reported in 

 Table VII. The soil for series i was from a "sand-soak " spot at Estero, 

 Fla. ; for series 2, from high pine land near Teesburg, Fla. ; and for series 

 3, from intermediate pine land at Orlando, Fla. These tests were made 

 by Miss Clara H. Hasse, of this office, dui'ing October and November, 

 1918, and through her courtesy are presented here. Only the i/i dilu- 

 tions are included in Table VII, since in each series the results from 

 higher dilutions were in accord with these. The percentages are based 

 on inoculation of 600 punctures. 



The first series indicates distinctly a retarded decline and prolonged 

 persistence in the dry soil. The second series, with another type, shows 

 no decided difference between the wet and dry. In the third series the 

 initial decline was more raoid in the drv than in the wet soil. 



