SOILS — PEETILI2ERS. .". i:; 



accompanied A.zotobacter in crude mannite cultures, was studied alone and in 



ation with one another or other organisms, in nutrienl media of differenl kinds 



I mannite and sodium malate solutions I and in Boils. 



The analytical results in case ol pure cultures shoM thai in the case of I . vinelandii 

 the fixation of nitrogen was al the rate of I to 5 nr_ r . of nitrogen forever) gram of 

 mannite consumed, while in the I. beyerincki and .1. chroococcum cultures the rate of 

 fixation was less than I mg. of nitrogen per gram of mannite consumed. 



" In the combinations, it appears thai Proteus vulgaris did nol appreciably affecl 

 the fixation by I. vinelandii, bul thai /■'. new jersey and /.'. pyocyaneus, both denitri- 

 fying bacteria, depressed it considerably, particularly in the case of the former. < n 

 the accompanying small bacilli, /<". SOa increased the fixation somewhat, B. 

 depressed it. B. 84 did no1 affecl it. and /.'. 85, or /.'. 85 and /•'. SOa togel ner, im 

 it. On the other hand, where B. SOa, B. SS, /»'. 84, and /;. 85 were all inoculated 

 together with I. vinelandii, there was no fixation at all by the latter." 



.1. beyerincki sin. wed uniformly a slighter nitrogen-fixing power than A. vinelandii. 

 The decay bacteria depressed the fixation of nitrogen. Tin- decrease was leasl in the 

 ease of Proteus vulgaris. Where />'. SOa was inoculated together with I. beyerincki, 

 thf fixation was greatly enhanced, the yield being 9.5 hilt, as compared with the 

 higher yield of the two inoculations with A. beyerincki alone. Where .1. beyerincki 

 was inoculated together with 11. S3, the depression was greater than in any other 

 combination. 



••The nitrogen-fixing power of .1. chroococcum in pure culture was practically the 

 same as that of .1. beyerincki. In the presence of other organisms, however, the 

 former showed somewhat differenl relations. There was an increased fixation here 

 in the presence of decay bacteria, as well as in the presence of />'. SOa, /.'. SS, /.'. 84, 

 and B. 85. In the presence of Proteus vulgaris, the yield of nitrogen was raised from 

 7.17 mg. to 8.55 mg.; in the presence of />'. new jersey it was raised to L0.23 mg.; in 

 the presence of B. SOa, to 9.16 mg.; in the presence of II. S3, t<» 8.55 mg.; in the 

 presence of /<'. 84, to 9. 'M m<r.; and in the presence of B. 85, to 10.38 mg., the highesl 

 yield in the series. . . . There was practically no fixation of nitrogen by .1. ",,<,</.■<- 

 tovmii, either when growing alone or together with the smaller bacilli. . . . 



"The small bacilli did not inerease the nitrogen content of the mannite solution 

 to any appreciable extent. When, however, they were inoculated together with A. 

 vinelandii they seemingly augmented the nitrogen-fixing power of the latter. . . . 

 The evidence, both microscopical and macroscopical, pointed to the fact that the 

 small bacilli can make more growth in malate solutions than in mannite solutions. 

 The analytical data confirm this evidence." 



In view of the results obtained " it is deemed justifiable to state that members of 

 the Azotobacter group are capable of fixing atmospheric nitrogen when growing in 

 pure culture, and that they are affected unfavorably by acid culture media until their 

 growth is entirely stopped, when the acidity reaches a certain limit. Beyerinck's 

 theory, therefore, that the fixation of A/.otohacter is symbiotic is proved untenable, 



and the fact that the developmenl of .1. chroococcum in nitrogen-] r solutions was 



made possible by other bacteria indicates, probably, that the latter produced an alkali 

 ami decreased the acidity of the culture solution, thus enabling the Azotobacter to 

 de\ elop normally." 



Chemical studies of mannite media in which .1. vinelandii had been grown showed 

 the presence of a small hut appreciable amount of nitrogen, in both young and old 

 cultures, not precipitated by lead acetate and a large proportion not precipitated by 

 phosphotungstic acid or tannic acid. Similar studies <»f Witte's peptone show '"that 

 a large proportion of the peptone nitrogen is precipitated neither by the sulphates 

 of the heavy metals nor by tannic acid. The nitrogen carried into the filtrate con- 

 sists in part of amido-acids, oramido-acid derivatives." 



