HINTS AND EXPERIMENTS 201 



Divide this by the weight of the untreated plants, 

 and subtract 100 from the answer. 



Thus, to work out the percentage increase in the 

 humogen-treated beans obtained by Mr. Holmes, 

 and described in the chapter on " The Testing of 

 Humogen," one would calculate as follows: 



x 100 _ 151 (half ounces) x 100 

 8J 8 1 (half ounces) 



.-. Percentage increase = 186*5 ~ *oo = 86*5 per cent. 



NOTE that experiments with radishes can be con- 

 ducted in the open at any time between the middle 

 of March and the first week in September. The 

 plants can be grown in a greenhouse or in a light 

 and airy room at any time of the year. 



MODEL EXPERIMENT II. 



Primula (any Variety). 



Primula plants ready for their final potting are 

 easily obtained in the early autumn. The new pots 

 should be filled (i) with good potting soil, as recom- 

 mended by nurserymen from whom it may be 

 obtained ; (2) with some rich mixture such as that de- 

 scribed in the chapter on " The Testing of Humogen," 

 as used at Kew, or according to what the experi- 

 menter regards as the best possible obtainable; 

 (3) the good potting mixture used for (i), with one- 

 ninth of humogen well mixed. From this time 

 ordinary cultivation is all that is necessary. 



