SOURCES OF THE CONSTITUENTS OF PLANTS. 463 



may doubtless be entirely attributed to carbonic acid, ob- s ources f rom 

 tained either directly from the atmosphere or furnished by which the con- 

 the gradual decay of humus in the soil. For the hydrogen plant" are de- 

 a double source may be assigned water and ammonia. rived - Ofcar- 

 The abundant occurrence of resins, oils, fats, in which this 



element preponderates, conclusively establishes the fact that 

 the supply of ammonia, as indicated by the nitrogenized compounds' 

 which have been formed, is insufficient to account for the quantity of hy- 

 drogen, and for which there would appear no other source than water ; 

 and though the most brilliant light, even though concentrated by a pow- 

 erful burning-glass, can not alone eifect the decomposition of this liquid, 

 there will be no difficulty in admitting that such a decomposition does 

 take place, when we recall that carbon is being presented in what might 

 be termed its nascent state. 



Of the nitrogen necessary for the formation of the protein bodies of 

 plants, it is generally concluded that ammonia is the only 

 source, and that these organisms do not directly obtain that 

 element from the atmospheric air; moreover, it occurs apparently to a 

 sufficient extent in their sap, having been introduced by absorption 

 through the roots. As essential to the production of the same group 

 of bodies, the protein substances, both sulphur and phosphorus are in- 

 troduced through the same channel, from the soil, as sul- of sulphur and 

 phates and phosphates, which undergo decomposition and phosphorus. 

 deoxidation within the organism, so as to yield the sulphur and phos- 

 phorus in an unoxidized state. 



We can not overlook the saline substances, or mineral bodies, which 

 occur in different parts of plants, and which obviously are of saline sub- 

 absolutely essential to their constitution. The circumstance stances. 

 that, in any given plant, they are found fixed in their nature, definite in 

 their quantity, and deposited in determinate regions, is sufficient to es- 

 tablish that conclusion. As is very well known, we can not judge of 

 their nature or condition during the life of the plant from the aspect they 

 present when its ash is examined. Thus those which have been exist- 

 ing as neutral or acid salts of organic acids must appear in the ash as 

 carbonates ; and though it has been established that basic and mineral 

 substances generally will to some degree replace one another nay, that 

 even the plant itself, by generating vegetable alkaloids, may dispense 

 with bases of the mineral kind, the extent to which this can be carried 

 is as yet undetermined. The occurrence of sulphates and phosphates 

 in the leaves and seeds, and wherever organic activity has to be dis- 

 played, and protein bodies are found, is sufficient to establish a con- 

 nection between those substances and the neutral nitrogenized bodies, 

 though of the manner in which, from carbonic acid, water, ammoniaj 



