CH. Xl] BACTERIA IN THE SEA 2G7 



can grow on unmanured soils and can produce a crop richer in 

 nitrogen than any other known to us. Further Kuhn, in 1901, 

 shewed that he had been able to raise good and increasing crops of 

 rye on one field for twenty years, and that more combined nitrogen 

 was taken from the soil than was precipitated on it from the 

 atmosphere. Obviously then the fixation of the elementary gas 

 must have been carried out in the soil. Berthelot shewed in 1885 

 that this fixation was probably due to the action of bacteria, and 

 just ten years later Winogradsky shewed, in his well-known memoir, 

 that such micro-organisms were actually present, and indeed were 

 very widely distributed in the soil. Now the nitrogen fixation of 

 the leguminous plants is affected by the activity of a bacterium, 

 Bacillus radicicola, which infests the nodular, gall-like swellings to 

 be found on the roots of the leguminous plants such as peas, 

 beans and clover; and the association of the two organisms, the 

 plant and the bacillus, is a symbiosis, that is a metabolic partner- 

 ship ; or a case of parasitism of the plant on the bacillary growth, 

 whichever view we choose to take — both have been advocated. The 

 plant furnishes the bacillus with a carbohydrate food — sugar ; and 

 the bacillus absorbs the atmospheric nitrogen, combining it with 

 oxygen, and the nitric acid after being combined with some base 

 is taken up by the plant. So much has been made out by a long 

 series of researches, but Winogradsky shewed that there were other 

 bacteria which lived independently in the soil, or in symbiotic 

 relationship with other micro-organisms, and that these microbes 

 also possessed the power of taking up the atmospheric nitrogen 

 and combining it with oxygen. Winogradsky called the bacterium 

 he discovered Clostridium. Soon afterwards Beijerinck followed 

 with the discovery of another nitrogen-fixing bacterium which he 

 called Azotohacter. So far such organisms were known only from 

 the land but in 1895 and 1896 Keutner and Keding investigated 

 the occurrence of both bacteria and found that they were present 

 also in the sea^. 



^ See Jost's Plant Physiology, Lecture XIX., for a general account of the 

 biology of Bacillus radicicola, and for an account of Winogradsky's researches on 

 Clostridium. Keutner's work is published in the Wiss. Meeresunters. of the Kiel 

 Kommission, Bd. viii. Abth. Kiel, 1905. He also gives a good account of the 

 literature of Clostridium and Azotohacter. Keding's work is contained in Bd. ix. of 

 the same memoirs. 



