SOURCE OF PLANT-NITROGEN. - 15 



up till this time. This was ' Eecherches Chimique sur 

 la Vegetation/ by Theodore de Saussure, one of the 

 most illustrious agricultural chemists of the century. 

 De Saussure was the first to draw attention to the 

 mineral or ash constituents of the plant; and thus 

 anticipate, to a certain extent, the subsequent famous 

 " mineral " theory of the great Liebig. The French 

 chemist maintained that these ash ingredients were 

 essential; and that without them plant-life was im- 

 possible. He also adduced fresh experiments of his 

 own in support of the theory, based on the experi- 

 ments of Bonnet, Priestley, Ingenhousz, and Senebier, 

 that plants obtain their carbon from the carbonic 

 acid gas in the air, under the influence of the sunlight. 

 He was of opinion that the hydrogen and oxygen of 

 the plant were, probably, chiefly derived from water. 

 He showed that by far the largest portion of the 

 plant's substance was derived from the air and from 

 water, and that the ash portion was alone derived from 

 the soil. To Saussure we owe the first definite state- 

 ment on the different sources of the plant's food. It 

 may be said that the lapse of nearly a century has 

 shown his views to be, in the main, correct. 



Source of Plant-nitrogen. 



There was one question, which, even at that remote 

 period in the history of the subject, engaged the atten- 

 tion of agricultural chemists viz., the question of the 

 source of the plant's nitrogen a question which may 



