June 1. 1920 Behavior of the Citrus-Canker Organism in the Soil 1 93 



from a total of 1,000 punctures, and on the eleventh and fourteenth days 

 4,000 puncture inoculations from the infusions were entirely negative. 

 The evidence of this experiment therefore points to a gradual dying 

 out of the canker organism in unsterilized soil, although in the sterilized 

 soil the canker bacteria are very active. 



EXPERIMENT II 



This experiment was undertaken to obtain all possible information 

 upon the condition of P. citri in orchard soils. 



Rain had fallen intermittently every day for 15 days. The Ellen 

 grapefruit tree selected for this experiment showed 100 per cent of the 

 leaves cankered, and in many cases the leaves had over 50 cankers 

 apiece — that is to say, the tree was badly affected with canker and a 

 drop of water could hardly fall to the ground from this tree without 

 having been in contact with cankers. 



During a violent shower, rain dripping from the leaves of this tree 

 was collected in five culture tubes. These tubes were then carried to the 

 isolation plots where citrus-canker had been excluded. From each 

 tube of the rain water five young, actively growing grapefruit leaves 

 were inoculated on upper and lower surfaces, each leaf being punctured 

 at the same time with 40 needle stabs. The heavily cankered grape- 

 fruit tree was then cut down and removed, and all fallen leaves were 

 removed from the ground. Soil from beneath the tree was then placed 

 in five culture tubes, infusions were made and taken to the isolation plots, 

 and five leaves were inoculated from each infusion. Forty punctures 

 were made on each leaf, and both upper and lower surfaces were coated. 



The twigs bearing the leaves inoculated with the infusion as well as 

 those inoculated from the drip water were wrapped in paraffin paper with 

 a piece of moistened cotton. The paraffin paper was then covered with 

 opaque paper. A muslin tent was spread over the soil about the stump 

 of the Ellen grapefruit tree after all fallen leaves had been removed. 

 The tent prevented infected leaves from being blown upon the soil but 

 allowed active play of rain and air as under normal conditions. The 

 percentages of infection are given in Tables III and IV. 



Table III. — Inoculations on young pummelo leaves from rain water collected from the 

 leaves of a badly cankered grapefruit tree 



