STUDIES OF PHOTO-SYNTHESIS IN MARINE ALG^E 123 



Keding's work is a continuation and development of the fore- 

 going, and the statement that the algse- 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 " sich 

 wenigstens in den in Betracht kommenden physiologischen Eigen- 

 schaften 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, Herman Fischer 1 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. 



It is to be regretted that we had not the results above quoted 

 before us when starting our series of experiments, and that in conse- 

 quence no special precautions were taken to exclude nitrogen-fixing 

 bacteria from our jars. Yet in our opinion it may be reasonably 

 assumed that their presence did not seriously affect the results 

 obtained, for the following reasons : 



1 . What we consider to be definitely proven as a result of these 

 and former experiments above referred to is the utilisation of solar 

 energy for the purpose of nitrogen fixation. Column 5 in the table 

 shows a marked difference in the amount of nitrogen fixed, according 

 as the seaweeds were exposed to sunlight, or kept in weak light, 

 or in the dark. It appears to us to be a point of secondary im- 

 portance whether that energy is so utilised by the alga itself or by 

 an associated bacterium. If the effects observed are to be ascribed 

 to the latter, it would be a novel experience to find a chlorophyll- 

 less organism so functioning in relationship to light, and the proof 

 that it could do so would be of unsurpassed interest in relation to 

 the problem of the origin of life in a chlorophyll- less world. 



2. It is to be noted that, in order to get nitrogen fixed in 

 appreciable quantities, previous observers have found it necessary 

 to grow their bacteria in appropriate culture media containing 

 small quantities of glucose, mannitol, or other organic compounds, 

 as well as the inorganic phosphates, etc. These media in due course 

 became turbid, and bacterial scums were formed. Our experiments 

 were carried out in pure sea water only, and, during the eight days 



1 " Das Problem der Stickstoffbindung bei Pflanzen," Ber. deut. bat. 

 Gesell., vol. xxxv. ? pp. 423-454 (1917). 



