[BERKELEY] MARINE BACTERIA 33 



It is probable that floating marine plants absorb their nitrogen 

 from ammonium salts, for, as has already been pointed out, the reaction 

 of sea-water is normally acid from the bicarbonates (and possibly 

 free CO2) in solution, and, arguing by analogy with soil organisms, it is 

 questionable whether nitrification would take place in these circum- 

 stances. Where the water contains chalk, or other carbonate, in 

 suspension the conditions would be suitable for nitrification. At 

 the sea bottom, for instance, where chalk is accumulating, or on 

 calcareous rocks, nitrification might be expected to take place provided 

 sufficient oxygen were available. Marine plants growing in such 

 situations may therefore obtain their nitrogen as nitrate and differ 

 in this respect from floating forms. 



Nitrogen Fixation 



If denitrification occurs to any considerable extent under normal 

 conditions in the sea the question of the existence there of a capacity 

 for the fixation of free nitrogen becomes a most important one, for, 

 if such capacity does not exist, it means that the stock of fixed nitrogen 

 on the earth's surface is being constantly depleted except in so far as 

 nitrogen fixation on land is making the loss good. Only two agencies 

 capable of fixing free nitrogen in quantity under the conditions existing 

 on land are known with certainty, both bacterial, the nodule-forming 

 bacteria {Psendomonas radicicola) living in association with certain 

 leguminous plants, and the free living soil bacteria of the groups 

 Clostridium, pasteuriajiiis and Azotohacter. Something akin to the 

 former of these two agencies seems to haVe been described by Keding 

 and Keutner^ in cases of marine bacteria living in association with 

 algae or plankton organisms, and to the latter agency in free-living forms 

 found on the sea-bottom close inshore. I have not been able to see 

 either of these papers, but gather from the reference made to them by 

 Drew that no free-living nitrogen-fixing organisms are described from 

 the open sea. 



Denitrification has not been found to be a factor in the conditions 

 existing in the sea where the samples dealt with in this paper were 

 taken. Nevertheless it seemed of interest to see whether any nitrogen- 

 fixing forms could be isolated from them. Accordingly they were 

 inoculated into media made up in the same way as those usually 

 used for the isolation of Azotobacter in examining soil, substituting, 

 of course, sea water for fresh water. The composition of the media 

 was as follows: — 



1 Keding, M., 1906. Wiss. Meeresunters, Vol. IX. Kiel. Keutner, J., 1905. 

 Wiss. Meeresunters, Vol. VIII. Kiel. 



