8 GEORGE HARRISON SHULL. 



suggested here, of making the equivalence of reciprocal crosses 

 a separate experiment. 



Finally, to show how appropriately this experiment repre- 

 sents the actual cross between the red and blue flower, dip the 

 red flower into boiling water a moment and then hold it in the 

 fumes of ammonia or dip it into a dilute solution of ammonia or 

 of sodium hydroxide. Similarly take the blue flower and dip 

 it into the boiling water, and then into a dilute solution of 

 hydrochloric acid, in this way demonstrating that the difference 

 between the blue and red flower is due simply to the fact that 

 the cell-sap of the blue flower is alkaline, and the cell-sap of the 

 red flower is acid. 



