6 THE SCIENTIFIC PRINCIPLES 



little variation in the composition of the ash of one 

 and the same description of seed, or other final pro- 

 duct, provided it be evenly and perfectly matured. 

 This fact alone, independently of what has been 

 established of late years in regard to the office or func- 

 tion so to speak of individual mineral constituents of 

 plants, would be sufficient to indicate the essentialness 

 of such constituents for healthy growth. 



Th. De Saussure, in his work entitled, * Eecherches 

 sur la Vegetation'/ published in 1 804, gave the re- 

 sults of the analyses of many plant-ashes, maintained 

 the essentialness of the ash-constituents, and pointed 

 out that they must be derived from the soil. He 

 a] so called attention to the probability that the 

 incombustible constituents so derived by plants from 

 the soil were the source of those found in the 

 animals which fed upon them. 



Yet such was the prevailing uncertainty on the 

 point, that Sir Humphrey Davy, in his lectures 

 delivered not long afterwards, deemed it not inap- 

 propriate to combat the idea that the earths found 

 in plants had been formed from any of the elements 

 existing in the air, or in water. After quoting the 

 results of an experiment of his own, in which he 

 attempted to grow oats without any supply of silica 

 beyond that contained in the seed sown, and referring 

 to the experiments of De Saussure, he says : — 



' As the evidence on the subject now stands, it- 

 seems fair to conclude, that the different earths and 

 saline substances found in the organs of plants are 

 supplied by the soils in which they grow ; and in no 

 cases composed by new arrangements of the elements 

 in air or water/ 



It is no longer doubted that the mineral or ash- 

 constituents of plants must be provided within the 



