44 NOURISHMENT OF PLANTS. 



generate all the constituent elements of plants. The 

 greater proportion of plants consist of non-azotized 

 substances (each composed of three elements) ; all 

 these may be produced from carbonic acid and wa- 

 ter, when the elements of the water combine with the 

 carbon of the carbonic acid. If this occurs, the oxy- 

 gen of the latter must necessarily be liberated, as the 

 following summary shows : — 



Carbonic Acid i Oxygen is set free by exhalation. 



is formed of J Carbon \ Hence may be and are formed : 



Water c Oxygen \ Vegetable fibre, starch, gum, sugar, 



£ is formed of } Hydrogen ' ^'at, oil, resin, etc. 



It is, however, also possible that not the carbonic 

 acid, but the water, in plants may be decomposed, so 

 that the elements of the carbonic acid may combine 

 with the hydrogen of the water ; and accordingly, that 

 the oxygen which plants exhale during day-light may 

 be derived from the water. The chemical process 

 would then, indeed, be different, but the result would 

 still be precisely the same as that just stated. 



If to the two nutrients above mentioned, the third, 

 ammonia, is superadded, all the primitive materials 

 are present which are required for the formation of 

 azotized (each composed of four elements) vegetable 

 substances, as is evident from the following table : — 



Carbonic Acid ^Oxygen is set free by exhaialion. 



is formed of ( Carbon ->> 



„, „ Hence may be formed : 

 Water / Oxygen I .. , , ,, 

 . „ , r. ) i vegetable albumen, vegetable case- 

 is formed of 5 ^ , r • i . i  in 



^ Hydrogen i ine, gluten, chlorophyll, vegetable 



A^^omA \ bases, etc. 



is formed of ( Nitrogen J 



