2l8 



Journal of Agricultural Research 



Vol. XIX. No. s 



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

 tions of three soil solutions at various intervals after the soils had been treated with lime 

 water, dilute sulphtcric acid, and distilled water, respectively, and inoculated with 

 P. citri 



This preliminary and very artificial series indicates a slight retardation 

 of decline in the alkaline soil and a distinct acceleration in the acid soil. 

 In the latter, one notes the low infection percentages for the i/i dilution 

 as compared with the i/io of the same series, or with the i/i of the 

 other two series. While there is quite generally a tendency for the i/i 

 dilution to give unexpectedly low results, the present instance suggests 

 that the rather high acidity of the first wash water vehicle may play a 

 part here in preventing infection. This matter calls for further experi- 

 mentation. Since the tendency of most citrus soils is toward acidity, 

 the evidence presented in Table IX is reassuring as to the decline of 

 P. citri in such soils, notwithstanding the very unnatural conditions of 

 the experiment. 



PERSISTENCE DEEP IN THE SOIL 



The tests for downward penetration were made by placing partially dry 

 soil in open pasteboard cylinders 3 inches in diameter and watering the 

 surface with a strong P. citri suspension until the whole was saturated. 

 Sections were made at proper intervals and samples taken with proper 

 precautions from the axis of the soil column. For vertical ascent the 

 cylinders were placed in a shallow pan containing the suspension of 

 P. citri. 



In an 8-inch column of Florida sandy soil sampled at 2 -inch intervals 

 on November 20, 191 8, downward penetration was shown to be very 

 uniform throughout. A 15-inch column of greenhouse potting soil was 

 tested October i, 1919, with similar practically uniform penetration, as 

 shown by sampling at 3-inch intervals. 



In Florida soil tested for vertical ascent, the capillary rise was 6 inches 

 during four hours. Two-inch samplings showed P. citri to be uniformly 

 distributed. 



