58 Prof. B. Moore, Messrs. E. Whitley, and T. A. Webster. 



expected increase in dried weight if all were converted into carbohydrate, 

 130 mgrm. ; expected increase if all protein, 100 mgrm. ; expected increase if 

 all fat, 80 mgrm. 



If next the increase in the nitrogen be considered, this amounts to about 

 3 mgrm. which corresponds to about 20 mgrm. of protein, the remaining 

 80 to 90 mgrm. fixed would therefore represent the carbohydrates and fats. 



Addendum on Nitrogen-fixing Bacteria. 

 Our attention has been drawn to the fact that three different observers* 

 have demonstrated that the surface of the ordinary large sea weeds is 

 regularly colonised by nitrogen-fixing bacteria, and it has been stated that 

 these bacteria have been identified with the nitrogen-fixing bacteria known 

 in soils. 



Eeinke states that nitrogen bacteria were found without exception on all 

 the marine algse of Heligoland sent to the Botanical Institute at Kiel for 

 examination. The thoroughly washed alga was placed in a suitable nutritive 

 medium and there followed a heavy development of Azotobacter and corre- 

 sponding fixing of nitrogen from the air. 



In Keutner's experiments small pieces of various algae were introduced 

 into a culture medium and in about ten days the fluid became turbid and a 

 scum was formed on the surface of the water and on the pieces of sea weed. 

 The bacteria could be identified in the slime on the algee. Experiments made 

 on fresh-water plants gave the same results. This observer definitely states 

 that the culture flasks were kept either in a closed chest or cupboard or in a 

 thermostat — that is to say, in the dark. 



Keding's work is a continuation and development of the foregoing, and the 

 statement that the algge-colonising bacteria are the same as those known in 

 soils can probably be traced to his finding that the Azotobacter of the Baltic 

 and that of the land " sieh wenigstens in den in Betracht kommenden physio- 

 logischen Eigenschaften identisch verhalten." This at least is the only 

 evidence that we are able to find for such a conclusion. 



With the above results before him, Hermann Fischerf is inclined to 

 attribute to the action of bacteria, in the majority of instances, such cases of 

 fixation of nitrogen by green plants as have hitherto been recorded, and holds 

 that in every case where a claim is made to have observed such fixation a 

 need exists for proof that the technique was perfect. 



* Eeinke, ' Ber. dent. bot. Gesell.,' vol. 22, p. 95 (1904) ; Keutner, ' Wissen. 

 Meeresuntersuch., Kiel,' vol. 8, p. 27 (1905) ; Keding, ibid., vol. 9, p. 275 (1906). 



t "Das Problem der Stickstofifbindung bei Pflanzen," 'Ber. deut. bot. Gesell.,' vol. 35, 

 pp. 423-454 (1917). 



