190 Journal of Agricultural Research voi. xix. No. s 



P. ciiri is able to live actively — that is, increase and multiply within the 

 soil; (2) whether it exists simply passively and does not increase and 

 multiply; or (3) whether it is killed within the soil. 



The problem has been attacked previously by the writer and other 

 investigators by attempting to plate out soil samples and thus show 

 the presence of the canker organism in the soil. These attempts have 

 usually given negative results. However, such negative results have been 

 inconclusive because of the large number of the soil organisms which 

 would appear in the plates, making it difficult to identify P. citri even 

 if it were present. Investigations were therefore undertaken at Lamao, 

 P. I., with the purpose of attacking this question with different experi- 

 mental methods. 



EXPERIMENT I 



Fifty-five culture tubes of orchard soil from Lamao were prepared. 

 These were autoclaved twice, one hour each time, at 45 pounds pressure, 

 24 hours intervening between periods of steaming. Fifty-five tubes of 

 the same soil were prepared but were not sterilized. Each tube of ster- 

 ilized soil was inoculated wdth 2 cc. of a heavy infusion of P. citri in 

 sterile water, precautions being used as far as possible to avoid contami- 

 nation. The tubes of unsterilized soil were inoculated each with 2 cc. of 

 the same infusion, all processes being identical except that one series of 

 tubes was sterilized while the other was not. 



Five of the sterilized tubes and 5 of the unsterilized tubes were taken; 

 portions were removed from each with a spatula (a separate spatula 

 being used for each tube) ; and infusions were then made from each of 

 these 10 portions. These infusions were made in dry sterilized test tubes, 

 but tap water was used for the liquid medium. Inoculations from each 

 infusion were made upon the upper and lower surfaces of five young, 

 actively growing pummelo ^ leaves. Citrus maxima (syn. C. grandis, C. 

 decumana) . Forty punctures were made in- each leaf. The leaves were 

 then bound in waxed paper with wet cotton to maintain a moist atmos- 

 phere. The whole was covered with opaque paper to prevent burning 

 by the sun. 



This procedure was repeated each day for a period of 15 days, a new 

 series of five tubes of sterilized soil and a nevv series of tubes of unsteri- 

 lized soil being used each day. The inoculation data and results are 

 given in Tables I and II. The percentages expressed are based upon the 

 number of positive takes resulting from the total of 200 punctures on 

 5 leaves. Where stomatal infections occur they are counted as wound 

 infections. 



1 Following the usage of W. T. Swingle in Bailey's Standard Cyclopedia of Horticulture, the term 

 IMunmelo is used in its usual East Indian sense to include varieties of Citrus grandis distinct from the 

 grapefruit group of the West Indiee and the United States. 



