48 THE STORY OF PLANT LIFE 



At the outset it should be stated that plants 

 cannot utilise solid food, but only matter in solution. 

 Secondly, it should be remarked that plants do not 

 obtain their nutriment from the elements them- 

 selves, but from compounds or salts that are found 

 in the soil water. This acts upon the organic 

 and inorganic substances in the soil, and prepares 

 them for use by the plant by a process of decom- 

 position. 



The salts used in looo c.c. of distilled water may 

 be potassium nitrate, i grm. ; sodium chloride, J grm. ; 

 calcium sulphate, J grm. ; magnesium sulphate, i grm. ; 

 calcium phosphate, h grm. ; and a trace of iron 

 chloride. 



It was the German botanist, Sachs, who first 

 invented this method of showing the requirements of 

 plants. Grown thus as a water-culture, a seed will 

 germinate and put forth roots, leaves, flowers, and 



even fruit. 



If the plant be chemically analysed it will be found 

 to contain half its weight of carbon after the water it 

 contains has been evaporated. The carbon was not 

 supplied in the solution, and has therefore been 

 derived from the air by the leaves and not from the 



roots. 



Of the six compounds added to the water it 

 can be found that all but sodium chloride are essen- 

 tial to the plant, for if one is left out or another 

 substituted the plant suffers, so that the six ele- 

 ments. Potassium, Nitrogen, Calcium, Magnesium, 



