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TRANSACTIONS AND PROCEEDINGS 



BOTANICAL SOCIETY OF EDINBURGH. 



SESSION LXI. ^^"^ ^^*^ 



ttOTANICAU 



Addeess delivered at the opening of the Session 

 BY Professor A. P. Aitken, M.A., D.Sc, President of 

 the Society. — 12th November 1896. 



THE NITROGENOUS FOOD OF PLANTS. 



In the year 1674 a very remarkable discovery was 

 made by John Mayow, viz. that the air, which from all 

 time had been regarded as an elementary substance, was 

 really a mixture of at least two gases — one of them was a 

 gas which enabled things to burn, and the other was one 

 that did not. Moreover, he found that the gas which 

 enabled things to burn, or which " supported combustion," 

 as it is commonly expressed, was also the gas that enabled 

 animals to breathe or that supported respiration, and that 

 the other did not. He carried his researches even further, 

 and found that this active gas, which he called the "nitrous 

 spirit of the atmosphere," took part in the making of acids, 

 though it was not sour itself, and also that it was contained 

 in large quantity in nitre or saltpetre. Strange to say that 

 discovery seemed to create no interest at the time, the story 

 of it was told to listless ears and it fell into oblivion. 



Exactly one hundred years later (1774) that same nitrous 



^ spirit of the air was discovered by Priestley, who called it 



" dephlogisticated air," and it was thereafter described by 



I Lavoisier, who called it " oxygen " or the acid maker. The 



other constituent had been discovered by Rutherford in the 



^ Botanic Garden of Edinburgh in 1742, and shown to be a 



^ gas that animals could not live in, and he called it 



" mephitic air." I do not know how it was that Professor 



IJutherford was led to make the experiment that resulted 



in this discovery, but it was a very satisfactory experiment, 



TRANS. BOT. SOC. EDIN. VOL. XXI. B 



