Nov. 1S96.] BOTANICAL SOCIETY OF EDINBURGH 



the Society during the present session some interesting 

 information on the recent advances of a practical kind that 

 have been made in the growth of plants, arising out of our 

 better acquaintance with the manner in which they obtain 

 their nitrogenous nourishment. 



I have already referred to the fact that four-fifths of the 

 atmosphere consists of free nitrogen gas. With such an 

 enormous store of nitrogen around them it would seem, at 

 first sight, that whatever difficulty plants might find in 

 obtaining the other constituents of which they are composed 

 they ought to experience no difficulty in obtaining an 

 abundant supply of nitrogen. Practical experience, 

 however, shows us very clearly that it is the constituent 

 most difficult for them to obtain, as it is the most expensive 

 for us to supply. The natural conclusion to arrive at from 

 that consideration is that the nitrogen of the air must 

 surely not be an available source of plant nourishment. 



Up to the present decade there w^as no dogma more 

 firmly rooted in the minds of botanists than this, that 

 plants could make no use of the free nitrogen of the air. 

 Careful experiments made by Boussingault, who was a most 

 accurate experimenter, and whose manifold experiments 

 may be said to have laid the foundation of agricultural 

 chemistry, seemed to prove that plants could not assimilate 

 free atmospheric nitrogen. 



No excuse is needed to ask you to look for a minute into 

 the details of one of his now classical experiments. 



