404 BACTERIAL DISEASES OF PLANTS 



phosphate has been added (Petri). Petri probably used the 

 acid phosphate. Very Ukely there are several strains of this 

 organism, all pathogenic, but somewhat different culturally 

 (see No. XIV). 



The organism according to my observations does not lose 

 virulence quickly on media. It is killed by 30 minutes exposure 

 to sunlight in thin-sown agar plates exposed bottom up on ice 

 (Fig. 314). Repeated in 1915, exposing for a shorter time, when 

 colonies appeared on the insolated half of the plates exposed for 

 5 minutes, but none on those exposed for 10 minutes (at 15°C.). 



Technic. — The parasite being abundant and active in cavi- 

 ties in the olive tubercle, its isolation offers no special difficulty 

 provided young undecayed parts are selected. The surface 

 should be scraped and then flamed or soaked 60 seconds to 5 

 minutes, depending on size of the piece, in 1 : 1000 mercuric chlo- 

 rid water. The piece selected should be crushed thoroughly in 

 bouillon, the bacteria being allowed to diffuse for an hour or 

 more before plates are poured, which should be both from the 

 tube containing the mashings and from two dilutions of the 

 same. Success in the first series of plates often depends on 

 the care with which the dilutions are made, not only in this in- 

 stance but in many others. Various contingencies must be 

 provided for, always, especially the two opposite possibilities: 

 a, great abundance of viable bacteria in the part selected, which 

 would make thick sowings undesirable, or, b, the opposite, which 

 would make thick sowings absolutely necessary. 



In making inoculations select rapidly growing soft shoots 

 and introduce the bacteria by pricking the shoots several times 

 with a delicate needle two inches below the growing-point, 

 being careful not to crush or tear the tender bark. Such shoots 

 should be selected as will continue to grow for a month or two. 

 For comparison inoculate some slow-growing shoots. Leaves 

 may be inoculated in the midrib, and in the parenchyma; they 

 should be less than half grown, but comparisons may be in- 

 stituted by inoculating full grown ones. 



Young streak cultures on slant agar or on potato cylinders 

 may be used for the inoculations. 



The writer made one unsuccessful attempt to inoculate 



