1 92 Elementary Biology. 



Importance. Like carbon, hydrogen, and oxygen, an 

 essential constituent of the same organic and inorganic 

 compounds already shown to enter into the formation of 

 protoplasm. 



Not only carbon, but also hydrogen, nitrogen, and 

 oxygen are, in the case of the saprophytes, parasites, and 

 carnivorous plants, obtained from the organic compounds 

 contained in the media in or on which they live. 



II. Essential elements in the plant organism, present 

 in small amount, 



SULPHUR. 



Origin. The sulphur is obtained by the decomposition 

 of salts of sulphur present in the soil. Undoubtedly the 

 chief salt from which the sulphur is procured is sulphate of 

 lime. This salt is probably decomposed by some organic 

 acid in the plant, such as oxalic acid, crystals of calcic- 

 oxalate being formed, the nascent sulphur combining with 

 higher compounds. Many other sulphates, such as those of 

 potassium, magnesium, and ammonium, are probably used 

 in this way. 



Importance. Although sulphur is itself volatile, it is not 

 burnt off during calcination, but is found in the form of 

 sulphuric acid united with bases present in the ash to form 

 sulphates. It forms an essential constituent of proteids and 

 many transition substances. 



PHOSPHORUS. 



Origin. Phosphorus, like sulphur, is obtained from its 

 salts present in the soil. These salts are mainly those of 

 lime, potash, and magnesia. 



Importance. Phosphorus, though present in very small 

 amount, nevertheless seems to be in some way essential to 

 the vitality of the organism. In addition to forming a 



