Dec. i 5 , 1920 Effect of Temperature and Humidity on Citrus-Canker 455 



At 5 C. a very small zone was noticed after several days, which in- 

 creased very slowly until at the sixth day the colony was just visible to 

 the naked eye. Growth at io° was first observed on the third day and 

 increased slowly with time. Growth at 20 , 25 , and 30 was, of course, 

 much more pronounced. No visible growth occurred at 33 to 35 and 

 38 to 40 , although some enzym action took place. 



The surfaces of the cylinders were slightly depressed at 20 C, the 

 depression increasing in depth at 25 and 30 . When the cylinders 

 were cut open, it was found that the clear zone proceeded down in the 

 shape of a cone, and its progress was almost as rapid as that of the zone 

 on the surface. 



At 25 and 30 C, where the organism grew over the whole surface and 

 down the sides, the decomposition of the upper half of the plug took 

 place. Examination for starch grains under the microscope showed that 

 none were present, while the middle lamella was completely dissolved, 

 the cells standing apart. From the results of the study of the enzym 

 action of Pseudomonas citri on soluble starch agar and steamed potato 

 plugs, we can conclude that it is a strong diastase secretor. Cytase is 

 also produced abundantly. 



The organism appeared to thrive longer and produce more enzym near 

 the critical temperatures on potato plugs than it did on the starch agar. 

 At 5 C. a small white zone was produced with a trace of growth. No 

 growth was visible at 33 to 35 or at 38 to 40 , although a rather large 

 depressed zone was distinctly noted. Potato plugs with no visible growth 

 in the 5 and 33 to 35 cases at the end of 8 days produced abundant 

 growth when transferred to 30 . However, plugs kept for 24 hours in 

 the 38 to 40 case when transferred to 30 produced no growth, nor 

 did the white zone increase in size. 



BEEF bouillon. — All the beef bouillon used in the experiments was 

 adjusted to +8 Fuller's scale, since it was found that the organism de- 

 veloped very well at this acidity. During the course of the work with 

 beef bouillon, no counts were made of the bacterial growth in cultures 

 at the different temperatures. 



By means of a bulb burette 10 cc. of the bouillon were placed in each 

 tube. The tubes were kept in the various cases overnight and were inoc- 

 ulated the next morning with a 2-mm. loop from a 48-hour-old culture of 

 Pseudomonas citri. Each day two tubes were withdrawn and a reading 

 was taken. 



Pseudomonas citri makes a very characteristic growth in beef bouillon. 

 Growth is first noticed by the clouding of the medium. After a few days, 

 flakes appear, followed by a yellow ring at the surface of the bouillon; 

 later, the flakes precipitate to the bottom. Thus, in Table IV, the 

 readings are based on the characteristic behavior of the organism. 



