196 HISTORY OF BOTANY 



Hansen, claimed to have demonstrated its presence, 

 while others, such as Gautier and Molisch, denied that 

 it occurred in the analysis of chlorophyll, a view that is 

 now accepted, although it is impossible to say in what 

 way the iron is really essential. I might quote to you 

 similar differences of opinion in relation to the functions 

 of every one of the metals and non-metals I have men- 

 tioned. Perhaps the truth is that all the "elements of 

 the ash play many parts, all co-ordinated by the living 

 substance of the organism." 



The Absorption of Nitrogen 



You will doubtless remember that in 1861 Boussingault 

 succeeded in demonstrating that the atmosphere' was* 

 not the source of nitrogen to the plant, but that all of 

 that element employed in metaboUsm was obtained 

 from salts of nitric acid and ammonia in the soilT) Experi- 

 ments similar in their nature to those carried out by the 

 French physiologist were conducted by Law.es and 

 Gilbert in England. Lawes, in the early years of the 

 century, had been investigating the values of certain 

 manures at Rothamsted in Hertfordshire, and had acquired 

 a consiaerable fortune from his patents for the production 

 of superphosphates. In 1843 Lawes invited Gilbert, 

 then a young man of twenty-six, who had studied chemistry 

 at Giessen under Liebig, to join him, and so began a 

 scientific partnership that lasted for fifty -eight years. 

 More than one hundred monographs were pubUshed 

 from the Rothamsted Institute between 1843 and 1901 

 in the joint names of the two investigators. The partner- 

 ship was an ideal one, for Lawes was the practical man 

 with a wide knowledge of the needs of agriculture, and 

 Gilbert possessed the scientific brain, trained in a famous 

 chemical laboratory, that could work out the best method 

 of achieving the result aimed at. 

 — ^ Before describing to you the fundamental advances 



