|   | 
        Plant height (cm) Samples 1-9 | 
         
      
        crude oil 
          concentration | 
        1 | 
        2 | 
        3 | 
        4 | 
        5 | 
        6 | 
        7 | 
        8 | 
        9 | 
       
      
        | 0%  | 
        17.90a  | 
        16.7a | 
          | 
          | 
          | 
          | 
          | 
          | 
          | 
       
      
        | 2% | 
          | 
          | 
        13.66a  | 
        9.06c  | 
        10.20bc  | 
        7.02d  | 
        11.25b  | 
        10.90b  | 
        7.15d | 
       
      
        | 3% | 
          | 
          | 
        9.80a  | 
        9.06a  | 
        10.00a  | 
        9.44a  | 
        9.90a  | 
        9.66a  | 
        7.20b | 
       
      
        | 4% | 
          | 
          | 
        10.00abc  | 
        7.50c  | 
        11.50a  | 
        7.75c  | 
        10.98ab  | 
        10.76ab | 
         8.60bc | 
       
     
    a, b, c................ within each row, means with the same letter are not significantly different p=0.05 |