CHAPTER III 



ASSIMILATION OF NITROGEN^ 



§1. The Nitrogen of the Air.— Atmospheric air is four-fifths free nitrogen 

 and it contains very small amounts of ammonia. We owe the first experiments 

 upon the assimilation of free nitrogen to Boussingault/ who grew various plants 

 from the seed in nitrogen-free, ignited sand to which was added some ash from 

 seeds of the kind of plants employed. He placed the porous culture pot in a 



shallow glass dish supported above the 

 bottom of a larger glass pan, in which- 

 stood a large bell-jar, covering the cultures. 

 (See Fig. 41.) Some sulphuric acid was 

 placed in the large pan, to prevent the en- 

 trance of ammonia from the outside air 

 into the bell-jar. Two glass tubes were 

 introduced under each jar, one to supply 

 distilled water' to the dish in which the 

 pot stood, the other to provide the necessary 

 carbon dioxide to the air-space' within the 

 bell-jar. There was thus no source of 

 nitrogen within the bell-jar, other than 

 the free nitrogen of the air. The amount 

 of nitrogen in the seed was determined, at 

 the beginning of the experiment, by analy- 

 sis of a control portion of the same kind 

 of seed. The apparatus was exposed to 

 light, and at the close of the experiment 

 (after two or three months) the nitrogen 

 content of the mature plant was deter- 

 mined, and no increase in this element 

 could be ' detected. It follows from this 

 that free nitrogen is not assimilated by ordinary higher plants when ihese 

 are cultivated in soU without microorganisms. 



>■ A complete summary of the work upon nitrogen assimilation up to 1879 is given in: Grandeau, L., 

 Cours d'agriculture de I'^cole forestidre. Chimie et physiologie applies k I'agriculture et k la sylviculture. 

 I. La nutrition de la plante. Paris, 1879.* 



» Boussingault, 1860-91. [see note 5, p. 2.] Idem, De Taction du salp^tre sur la vfig«- 

 tation. Ann. sci. nat. Bot. IV, 4: 32-46. 1855. Idem, Recherches sur ripifluence que 

 I'azote assimilable des engrais exerce sur la production de la matiere v6g6tale. Ibid. IV, 7 : 

 S-20. i8s7.—Ed. 



' It should be mentioned, however, that, while distilled water should not add anything but 

 water and the atmospheric gases to the organism, yet it may extract other materials. Thus 

 seedlings grown in distilled water give off salts, etc., by diffusion into the surrounding medium. 

 (See, further, note b, p. 77.) — Ed. 



60 



Fig. 41. — Arrangement of Boussin- 

 gault, for growing a plant in nitrogen-free 

 soil, without access of ammonia from the 

 air. The large pan contains sulphuric 

 acid (forming a seal);' water is .supplied 

 through the tube at the right and carbon 

 dioxide through the one at the left. 



