328 The Physiology of Plants BOOK in 



Some experiments made by Schloesing and Laurent in 

 1891 claim attention next, as they appeared to contradict 

 Boussingault as far as particular plants are concerned. 

 They cultivated certain plants belonging to different natural 

 orders, supplying them with free nitrogen, which was 

 measured at the beginning and at the end of the experi- 

 ments. They found that in some cases a certain amount 

 was appropriated. In them all they observed that the 

 growth of the plant was associated with the presence of 

 lowly forms of algae and mosses spreading over the surface 

 of the soil. They attributed the fixation to these and not 

 to the culture plants, and showed that it only took place 

 under a free exposure to light and air. 



These statements met with some criticism from Armand 

 Gautier and Drouin, who claimed to have noticed the same 

 phenomenon, but who put forward a different interpretation. 

 They attributed the fixation to the microbes in the soil ; 

 they held that aerobic microbes in oxidizing organic matter 

 oxidize and fix a little nitrogen ; while anaerobic forms 

 produce from it ammonia and amidogen compounds. These 

 are stored by the algae, so that the lowly green vegetation 

 acts only indirectly, while the microbes fix the nitrogen 

 of the air. 



Considerable controversy ensued, maintained during 1892 

 by Berthelot on the one hand, claiming that the action is 

 exclusively bacterial, and by Schloesing and Laurent on 

 the other, maintaining that it is confined to the surface of 

 the soil and is due to the lowly green vegetation flourishing 

 there. 



Passing over the work of Breal, and some other writers 

 of the time who really added nothing new, some experi- 

 ments of Kossowitsch in 1894 have considerable value as 

 tending to reconcile the apparently discordant results. 



He used in his first experiments pure cultures of Cysto- 

 coccus, which he cultivated in special apparatus and sup- 



