264 AZOFICATION 



of carbon in red clover. He obtained for other substances the 

 following results: 



1456.5 mgm. of nitrogen per 100 gm. as glucose. 

 280.4 mgm. of nitrogen per 100 gm. as cornstalks. 

 596.8 mgm. of nitrogen per 100 gm. in stalks and root residues of 

 corn. 



325.4 mgm. of nitrogen per 100 gm. in wheat straw. 



The carbon nitrogen ratio in compounds is no indication of their 

 value to nitrogen-fixing organisms, for non-leguminous hays and 

 straws are utilized just as effectively as are the legumes. Mockeridge 

 found that the ratios of nitrogen fixed to the heat of combustion with 

 the four lower fatty acids is almost constant. The same holds true 

 with starch, dextrin, and gum arabic, when allowance is made for 

 experimental error, which is greater with these compounds than 

 with the simpler compounds. This close relationship is not, how- 

 ever, graduated and no such uniformity is observed with the series 

 of monohydric alcohols. 



The quantity of nitrogen fixed per gram of carbohydrate varies 

 greatly with the species. Winogradsky found Clostridium pasteuria- 

 num to assimilate 2 to 3 mgms. of nitrogen for each gram of sugar. 

 But this like other anaerobic organisms is very wasteful of energy, 

 leaving much of it in the butyric acid, acetic acid, and butyl alcohol 

 formed. In the experiments of Bredemann with B. amylobacter and 

 of Pringsheim with Clostridium americanum, the amounts fixed were 

 at times much larger. Much greater fixations have been reported 

 with Azotobacter, and Lipman has obtained as high as 15 to 20 mgms. 

 of nitrogen per gram of mannite assimilated by A. vinelandii. This 

 quantity is considerably greater than that fixed by any of the other 

 members of the group. 



Koch and Seydel claim that the usual method of estimating the 

 nitrogen-fixing powers of Azotobacter is erroneous, as it does not 

 represent accurately the intensity of the process. In a series of 

 experiments made by them, the amounts of nitrogen fixed per gram 

 of dextrose used were 53, 70 to 80, 20 to 30, and 5 to 8 mgms. on the 

 first, second, third, seventh, and eighth days, respectively. 



Krainsky considers that there should be sufficient organic matter 

 in the soil to permit that for 1 part of nitrogen formed there will be 

 90 parts of carbon for the use of the organism. The organisms, how- 

 ever, utilize the carbohydrates more economically when only small 

 quantities are present. Walton finds with Indian soil that highest 

 fixation is obtained per gram of mannite when 10 grams are used in 

 1 liter of nutritive solution. Young, vigorously growing cultures 

 usually fix more nitrogen than the older ones. The nitrogen fixed 

 is greatest in the first stages of the growth of the organisms, as is 

 seen from Fig. 33 from the work of Omelianski. 



v The efficiency of these organisms is, therefore, greatest when they 



