430 Annrdversary Address. 



constituent of which they ave most largely composed) on 

 the carbonic acid, which is alwaj 7 s present in the atmosphere. 

 This gas, plants have the power, through their leaves, quite 

 as much as by their roots, of decomposing — assimilating 

 the carbon, and liberating the oxygen of which it is 

 composed. This discovery of Leibig's brought to light 

 that beautiful harmony of nature, the interdependence of 

 vegetable and animal life. How carbonic acid gas, so 

 noxious to animal life, which is generated by every breath 

 that is drawn, by every fire that burns, by every organism 

 that decays, forms the source from which vegetable life 

 derives, in much the greatest part, the constituents with 

 which to build up its structure. How plants not only 

 purify the atmosphere and render it fitted to sustain 

 and nourish animal life, but actually convert a poison 

 into wholesome food for its further sustenance and increase. 

 He also showed by the analyses of the ashes of plants, 

 that some mineral constituents were always present, and 

 that without a due proportion of these existing in an 

 assimilable condition in the soil, from whence alone they 

 could be obtained, plants could not thrive and produce the 

 results aimed at by cultivators. That accordingly, degrees 

 of fertility in soils were ascribable to the presence or absence 

 of these mineral constituents, in an assimilable condition ; 

 but as soils in general contained an abundance of the 

 majority of the mineral constituents necessary, it was 

 almost wholly upon the presence of phosphorus and potash 

 that their fertility depended. 



Leibig, unfortunately for his otherwise most distinguished 

 reputation as an Agricultural Scientist, advanced and 

 maintained the theory, that plants obtain the nitrogen, 

 they all contain in larger or smaller quantity, solely from 

 the atmosphere, having the power, as he asserted, of 

 assimilating it much in the same way as they do carbon. 

 This error of his led him to minimise the value of nitro- 

 genous manurial applications, and to overestimate the value 

 of phosphatic. 



In spite of this error, perhaps it might be added quite as 





