THE AMERICAN BOTANIST. 51 



ing grain it invariably kills out the weeds without harming 

 the other plants. At first glance this seems a preposterous 

 statement since it is naturally assumed that what will kill weeds 

 ought to kill other plants. The explanation, however, is this : 

 The leaves of our grains are covered with a fine coating of 

 wax, called bloom, which sheds the chemical when sprayed 

 upon it, while the leaves of most weeds, lacking such protec- 

 tion, are burned up in consequence. The sulphate of iron is 

 likely to have no effect on weeds whose leaves are protected by 

 bloom and will kill field crops lacking the protection. 



Flower Pigments. — It begins to look as if the great 

 range in the color of flowers, which renders them so attract- 

 ive to us, is merely a matter of a few chemicals. C. M. Broom- 

 all has been experimenting along these lines and in the "Pro- 

 ceedings of the Delaware County Institute of Science" for 

 January, notes that in general an alcoholic solution of the 

 petals of red and pink flowers will turn green when alkali is 

 added and red if acid is used; yellow, purple and blue flowers 

 turn green with alkali but resume their original colors when 

 acid is applied. The experimentor finds sodium hydroxide 

 and nitric acid to be satisfactory reagents, though other acids 

 and alkalis may be used. Care should be taken not to add an 

 excess of the reagent. If this is observed, the solution of a 

 given flower may be turned to green and back again a num- 

 ber of times by making the solution alternately acid and al- 

 kaline. It is concluded from these experiments that the flowers 

 have but three pigments, red, yellow and blue, from which by 

 various combinations all the other colors can be made. In 

 nature, the evolution of carbon-dioxide in the flower is sup- 

 posed to give the necessary acid for slowly changing the color 

 of the greenish buds to that of the mature flower. The pig- 

 ment appears to be present in the flower-buds even while yet 

 green, for if they are placed in weak acid solutions at this 



