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The plcmt food in the soil 



43 



Figs. 20 and 21 are photographs of sets of plants 

 grown in this way ; the weights in grams were ; — 



Fig. 21. 

 Mustard growing in surface soil (Pot 8), subsoil (Pot 4), sand (Pot 6) 



The plants in the soil remained green and made 

 steady growth. Those in the sand never showed any 

 signs of getting on, their leaves turned yellow and 



