96 



SCIENCE 



[N. S. Vol. XXXVIII. No. i 



or function of B. radicicola as it occurs in 

 nature. Within the past three years two 

 authors, employing widely different methods, 

 have attempted to supplement this rather 

 meager information. With a rather compre- 

 hensive plan for tracing the functional ac- 

 tivity presumably of nodule-forming bacteria 

 from the soil, through pure culture conditions, 

 and into root nodules again Gage' apparently 

 confused himself with a variety of seemingly 

 incompatible results, and by his unusual selec- 

 tion of descriptive terms heightened the in- 

 definite character of his report ; but even if his 

 conclusions were absolutely correct no real 

 advance has been made in our knowledge of 

 the life history of B. radicicola. 



A synthetic medium has been developed by 

 Grieg-Smith,^ who states that it is almost 

 specifically selective for Rhizohia. It should 

 be noted that Rhizohia is not defensible as a 

 generic designation for Bacillus radicicola.^ 

 If the selective phenomenon of this culture 

 medium were consistent for wide variations of 

 soil flora and soil type, we should have in this 

 medium a means for determining the approxi- 

 mate numbers of B. radicicola in any soil and 

 their relation to other members of the micro- 

 flora of the soil. The agar medium as de- 

 scribed contains levulose, asparagine, sodium 

 citrate, potassium citrate and tap water. At 

 the time of using from 0.06 to 0;10 cubic centi- 

 meters of normal sodium carbonate is added 

 to 10 cubic centimeters of the agar. 



Plates of a medium prepared by these cri- 

 teria were exposed to the air in the laboratory 

 at Washington for 15 minutes. An average 

 of four species of molds to the plate developed ; 

 also numerous species of bacteria, some of 



'Gage, G. E., "Biological and Chemical Studies 

 on Nitroao Bacteria," Centralblatt fiir Bakteri- 

 ologie, Parasitenhunde und InfeMionsTcrankheiten, 

 2. Abt., Bd. 2'i, No. 1/3, pp. 7-48, 1910. 



' Grieg-Smith, K., ' ' Determination of Bhizoiia 

 in the Soil," Centralblatt fiir BaTcteriologie, Para- 

 sitenhunde und InfelctionsTcranlcheiten, 2. Abt., 

 Bd. 34, No. 8/9, pp. 227-229, 1912. 



^ Kellerman, Karl F., ' ' The Present Status of 

 Soil Inoculation, ' ' Centralblatt fiir BaTcteriologie, 

 FarasitenTcunde und InfeTctionsTcrankheiten, 2. Abt., 

 Bd. 34, No. 1/4, pp. 42-50, 1912. 



which were chromogenic. In order to com- 

 pare the growth of molds in other media, there 

 were exposed in various places in the labora- 

 tory petri plates containing beef agar, the 

 nitrogen-free agar developed by us for isola- 

 ting B. radicicola* and Grieg-Smith's agar 

 made with and without the addition of sodium 

 carbonate. Table I. shows the results of these 

 tests. 



TABLE I 



Number of Species of Molds Developing upon 

 Various Media ^ 



Further tests were made by inoculating 

 various cultures of bacteria into Grieg-Smith's 

 agar, with the sodium carbonate added. Tubes 

 of slanted agar were used and the organisms 

 were streaked over the surface. The follow- 

 ing organisms grew : 



Sulphur yellow bacillus. 



Bacillus coli, 



Bacillus cloaca, 



Micrococcus roseus. 



Bacillus rossica. 



Bacillus prodigiosus. 



Staphylococcus aureus, 



Bacillus mycoides, 



Asotobacter beyerincTcii (on petri dish), 



Asotobacter chroococcum (on petri dish). 



The following organisms did not grow: 



Bacillus subtili-s, black variety, 

 Bacillus radicicola isolated from vetch nodules, 

 Bacillus radicicola isolated from Ceanotlms nodules, 

 Bacillus radicicola isolated from Cycas nodules. 

 Bacillus radicicola isolated from lima-bean nodules. 

 Bacillus radicicola isolated from alfalfa nodules. 



*Tap water, 1,000 c.c; cane sugar, 10 grams; 

 monobasic potassium phosphate, 1 gram; mag- 

 nesium sulphate, 0.2 gram; shredded agar, 15 

 grams, with reaction adjusted to -1- 4 Fuller scale. 



'Petri dishes opened for 15 minutes in the labo- 

 ratory rooms at different times during the day. 

 The figures are the averages of two plates for each 

 exposure. 



