Elementary Composition of Plants 7 



The plant derives all of its substance from soil and 

 air. Those derived from the air are known as organic 

 elements, and those derived from the soil as inorganic. 

 These terms are somewhat confusing, since in a certain 

 sense the soil-derived substances are organic when form- 

 ing a part of an organized body. They are, however, 

 usually classified as organic elements derived from the 

 air and inorganic elements derived from the soil, as 

 follows : 



The four so -called organic elements are derived 

 directly (or indirectly through the soil) from the air. 

 These return almost entirely to the air when a plant is 

 burned, while the remaining ten are mainly left in the 

 ash. 



The elements derived from the air constitute about 

 ninety-five per cent of all vegetable substances, and yet, 

 with the exception of nitrogen, we are not concerned 

 with their supply. While this is primarily derived from 

 the air, plants secure their supply either from substances 

 containing it in the soil or, as is the case with legumes, 

 from the air imprisoned in the soil. 



