722 EXPEEIMENT STATION RECORD. 



As a result of these investigations it appears tliat different soils vary widely 

 in their power to fix atmospheric nitrogen, this ranging from 0.15 to 14.47 mg. 

 of nitrogen per gram of mannit consumed. 



Mannit and lactose proved to be the best sugars for maximum fixation in 

 impure cultures. In pure cultures mannit and dextrin yielded the best results, 

 while sucrose gave a high degree of fixation with a pure culture, but only 

 slight fixation in impure cultures. 



The efiiclency of the Azotobacter as measured by the amount of nitrogen fixed 

 per gram of carbohydrate consumed is much increased in the presence of small 

 amounts of carbohydrates. 



Di-calcium and tri-calcium phosphate (in impure cultures, at least) gave better 

 results as regards fixation than the mono-salt. In determining the coefficient of 

 nitrogen fixation of any soil, it is important to consider the period of incuba- 

 tion, as losses in nitrogen will occur if the period is too long, and the deter- 

 mination of the nitrogen content of such cultures will not represent the actual 

 amount fixed. The incubation period for impure cultures was found to range 

 from 14 to 28 days. 



The amount of calcium carbonate needed is very small, and appeared to be 

 present in the soil tested in sufiicient quantities for the needs of the Azotobacter. 



The protein and phosphorus content of the Azotobacter cells is apparently 

 influenced by the age of the cultures, ranging for the protein from 8.31 to 19.13 

 per cent, and for the phosphorus from 2.51 to 2.97 per cent P^Os. 



For abundant development in pure cultures in liquid media, and to secure an 

 ample supply for chemical analysis of the dry Azotobacter cells, the new methods 

 previously described (E. S. R.. 22, p. 724) were used. 



On the influence of humus material in urea decomposition, 11. R. Christen- 

 SEN (CcntW. Bakt. [etc.], 2. AM., 27 (1910), No. 13-16, pp. 336-362, figs. 2).— As 

 the result of a large number of experiments, the author claims that the presence 

 of humus or humic acid exerts a very favorable influence on the decomposition 

 of urea. 



This disintegration of the urea results in the formation of ammonia, and is 

 brought about by a new species of bactei-ia (UroMciUus heijcriuckii n. sp.), 

 which is able to utilize the humus as a source of carbon. 



A technical description of the new bacterium is appended. 



Effect of previous heating of the soil on the growth of plants and the 

 germination of seeds, F. Fletcher (Cairo Sci. Jour., 4 (1910), No. Ji3. pp. 

 81-86, ph i).— Previous investigators (E. S. R., 19, p. 1120; 22, p. 121) have 

 claimed that the increased growth in partially sterilized soils was due to the 

 multiplication of ammonia-producing bacteria, but the author states that as 

 their plants were not grown in soils that had been completely sterilized there 

 would appear to be some doubt as to the correctness of their conclusions. 



To test this he heated soil to 95° and 170° C, the temperatures being main- 

 tained for two hours, after which the water content of all the samples was 

 made equal, and maize, previously germinated, planted in the soils. A decided 

 increase in growth was noted for the partially and completely sterilized soils 

 over the check plants, in length of plumule, general vigor of plant, and average 

 green weight. 



The author claims that it is more probable that the effect of sterilization is 

 due to the destruction by heat of toxic substances excreted by plants than to 

 an increased number of bacteria and an increased amount of ammonia. 



The effect of heating soil on germination was investigated, a previous investi- 

 gator having pointed out the retarding effect of heated soil (E. S. R., 20, p. 737). 

 In these experiments the author subjected soil to a temperature of 185° under 

 pressure, after which lupine, Alexandria clover, and sesame seeds were placed in 



