SOURCES OF ELEMENTS PLANTS REQUIRE 



35 



r0er 



grew. About 290 years ago it was thought that a plant was 

 nothing more than water that had undergone a naysterious change 

 in the soil. Only 



within compara- ^^ 



tively recent years ^^^^ 



has it been found 

 that the chemical 

 composit ion of 

 plants is quite simi- 

 lar to that of soils. 



The elements 

 required fey plants 

 and without which 

 they cannot grow 

 are ten in number; 

 viz., nitrogen, phos- 

 phorus, potassium, 

 calcium, mag- 

 nesium, sulfur, iron, 

 carbon, oxygen and 

 hydrogen. All the 

 mineral elements 

 are to be found in 

 ashes. 



Silicon, sodium, 

 aluminum and 

 other elements are 

 found in ash but 

 they are not neces- 

 sarily essential to 

 plant growth, since 

 plants can grow 

 without them. Ash, 

 then, is the mineral 

 portion of plants. 



Sources of Ele- 

 ments Plants Re- 

 quire. — Plants 

 secure the elements they require from the following sources: 



1. The soil — ^fmrnishing nitrogen and mineral elements. 



2. The soil water — ^furnishing oxygen and hydrogen. 



3. The air— furnishing carbon and oxygen. 



Fig. 15 — The root system of a potato plant in a per- 

 meable soil. This also illustrates the sources of the elements 

 required by plants (After Rotmistrov ) 



