Nov. 1896.] BOTANICAL SOCIET^^ OF EDINTBURGH 19 



presence of minute unicellular alg;B, which they found to 

 be the active agents in that fixation. 



That being so, there is no end to the possibilities of 

 nitrogen assimilation by plants, for these unicellular plants 

 resemble the cells of which most plants are composed, and 

 it may yet be found that all plants possess in some 

 degree, however small, the power of assimilating free 

 nitrogen by their leaves. In most cases such power of 

 assimilation may be so small in comparison with the 

 demands which the plants make upon the nitrogenous 

 matter in the soil, as to entirely escape observation until 

 some specially devised methods of detecting and determining 

 it are provided. 



Before closing my remarks I would ask you to recall the 

 results I have already referred to that were obtained by 

 Georges Ville. He knew nothing about the nodules on the 

 roots of the leguminous plants he grew, nor did he know 

 what was the modus operandi by which the plants he 

 worked with obtained their nitrogen, but he discovered the 

 main fact, that they did assimilate free nitrogen,^ and that 

 the power to do so was not confined to the papilionacese, 

 but shared by plants of other orders. Moreover, he laid down 

 quite accurately the conditions under which that assimila- 

 tion took place. And as it is right that those who have 

 been pioneers, and who have made important discoveries, 

 should get full recognition, it is important to recall the fact 

 that Ville's discovery was made forty-five years ago, and 

 that his experiments were not matters of doubt or hear- 

 say, but experiments whose results are all carefully and 

 accurately recorded. 



I have called this paper "The nitrogenous food of plants." 

 It might be expected that I should proceed to describe in 

 detail the various forms in which nitrogenous matters are 

 provided for plant food. Any such description would far 

 exceed the bounds of time at my disposal and of the 

 patience at yours. I need only say in a sentence that 

 numerous as the forms of nitrogenous food are, they are 

 convertible into one very soluble form — nitric acid — which 

 is believed to be the form in which chiefly, if not solely, 

 plants take up their nitrogenous nourishment from the 

 soil. Moreover, it is known that there are processes going 



