THE AMERICAN BOTANIST 



51 



lacks the waxy coat. \Mien the fields are sprayed, therefore, 

 the sulphate of iron runs off from the grain leaving it un- 

 harmed, while it remains on the mustard plants and soon causes 

 their death. 



The use of the sulphate of iron illustrates the way in which 

 large industries find markets for their waste products. Origi- 



Sprayed and unsprayed strips of grain. 



nally the iron sulphate, which is produced in cleaning wire for 

 drawing was turned into the rivers and streams until the steel 

 mills were ordered to discontinue the practice. In seeking a 

 market for the product its use as a spray was discovered and 

 now certain mills actually manufacture the sulphate of iron 

 since there is not enough of the by-product produced to supply 

 the demand for it. 



