322 Journal of Agricultural Research voi. xvi, No. u 



spore formers were transferred to agar slants, as were a representative 

 number of colonies of other types. About 97 per cent of these cultures 

 grew and were subsequently examined under the microscope for spore 

 formation. 



Table IV, which contains the recorded data from this experiment, 

 shows that of the 254 organisms from the open pots which grew after 

 isolation, only 2.8 per cent were spore formers, and of the 160 organisms 

 from the flasks which grew after isolation only 1.8 per cent were spore 

 formers. And this despite the fact that a special effort was made to 

 include all those colonies whose appearance suggested that they might 

 be spore-forming organisms. 



GROWTH OF PSEUDOMONAS FLUORESCENS AND PS. CAUDATUS COM- 

 PARED WITH THE GROWTH OF BACILLUS CEREUS IN STERILIZED 

 MANURED SOILS 



The organisms selected for the rest of the work were two non-spore 

 formers, Pseudomonas fluorescens (Fliigge) Migula and Ps. caudatus 

 (Wright) Conn, and a spore former, Bacillus cereus Frankland.^ The 

 first two organisms are described in the second section of this article, 

 and were chosen because of the frequency of their occurrence in manured 

 soil. B. cereus, according to Conn (9) and Laubach and Rice (27), is a 

 typical spore former occurring in soil and was selected for the purpose of 

 comparison with these organisms. 



SOIL INOCULATED WITH THE THREE ORGANISMS SEPARATELY 



In the series of experiments designed to show the relative rates of growth 

 of the three organisms under investigation, manured soil was sterilized 

 in flasks and inoculated with pure cultures in suspensions of carefully 

 determined strength. Samples from each series were plated at similar 

 intervals, and an effort was made to make all results comparable. 

 Microscopic counts were made of all the samples of soil inoculated with 

 B. cereus in order to determine the number of vegetative cells actually 

 present in the soil. As Ps. fluorescens and Ps. caudatus, on the other 

 hand, grow well on plates, form no spores, and show no tendency to 

 clump, a microscopic count of them was not so important as the plate 

 count, and since they are so small as to be easily overlooked under the 

 microscope a microscopic count proved even less accurate than the plate 

 count. The results as set forth in Table VI, Experiment I, show that 

 Ps. caudatus increased from a 13,300,000 plate count on the day of 

 inoculation to a 1,720,000,000 count seven days later, or an increase of 

 132 times the original inoculation. The initial plate count of Ps. 

 fluorescens was 4,390,000, and on the seventh day the count was 475,- 

 000,000, an increase of no times the original count. B. cereus, on the 



' As identified by Conn. This organism agrees with the descriptions of Chester (2, p. 27S), and I.aiuence 

 and Ford (25, p. 284-2S7). 



