July 18, 1913] 



SCIENCE 



97 



The growth of pure cultures of B. radicicola 

 on this medium was further tested by the 

 usual methods of poured plates in petri dishes. 

 The relative suitability of the diiierent media 

 is shown in Tables II. and III. 



Growth of B. radicicola in Grieg -Smith's 

 Synthetic Media 



Comparative Suitability of Different Media for 

 the Growth of B. radicicola 



Following' the technique outlined by Grieg- 

 Smith, direct isolation of B. radicicola was 

 attempted from soil of three types : (1) soil 

 used in potting plants at the Department of 

 Agriculture greenhouses; (2) soil from Akron, 

 Colo., taken from around the roots of Astra- 

 galus falcatus Lam., and known by check ex- 

 periments to be able to inoculate the roots of 

 Astragalus sinicus Linn.; and (3) soil from 

 Ithaca, N. Y., which had been sterilized and 

 inoculated with B. radicicola isolated from 

 alfalfa nodules. The ordinary dilution tech- 

 nique was employed and dilutions of 1 : 100, 



° This test was made with New York soil fur- 

 nished by Dr. B. M. Duggar, which he sterilized 

 and then inoculated with a strain of bacteria iso- 

 lated at Cornell University from alfalfa nodules. 



' This test was made with District of Columbia 

 soil which was sterilized and then inoculated with 

 alfalfa bacteria, strain No. 134. 



1 : 10,000 and 1 : 1,000,000 were taken. The 

 agar was used with and without sodium car- 

 bonate, and the plates incubated five or six 

 days at room temperature. 



The greenhouse soil developed molds and 

 various kinds of nonchromogenic bacteria on 

 both media ; on the media with sodium car- 

 bonate the Colorado soil developed molds and 

 various kinds of nonchromogenic bacteria, 

 while the media without the sodium carbonate 

 gave an almost pure culture of one species; 

 the New York soil gave pure plates with both 

 agars. In observing these plates it was very 

 noticeable that the agar with the sodium car- 

 bonate showed fewer colonies than the agar 

 without it; this has been noticed in regard to 

 both pure and mixed cultures. 



The colonies selected for final test were 

 those which resembled pure cultures of B. 

 radicicola. The bacteria isolated from New 

 York soil and from greenhouse soil were 

 tested for their ability to infect alfalfa, and 

 those from the Colorado soil were tested for 

 their ability to infect Astragalus sinicus. 

 These selections for tests were made because 

 of previous empirical determinations of the 

 inoculating power of these soils. 



The tests were conducted in sand nearly 

 devoid of nitrogen, moistened with Sach's 

 solution from which the nitrogen compounds 

 were lacking. Special glass jars designed to 

 prevent contamination were employed for 

 sheltering the plants which were grown from 

 disinfected seeds. The plants grew well, con- 

 sidering the abnormal conditions to which 

 they were subjected. At the expiration of 

 63 days the plants were taken from the jars 

 and the roots carefully washed. Table IV. 

 shows the inoculating power of the colonies 

 selected from the petri plates of Grieg- Smith 

 agar. 



TABLE IV 



Inoculating Poiver of Bacteria from Various Soils 



Isolated upon Grieg-Smith Agar 

 Plant Source Inoculation 



Alfalfa New York soil + 



Alfalfa Greenhouse soil — 



Alfalfa Uninoculated — 



Astragalus sinicus . . Colorado soil — 



Astragalus sinicus . . Uninoculated Plants died. 



