4 Diseases of Economic Plants 



covered with a sifting of powder made of "dry powder of 

 wood ashes, mixed with the sixth part of the same quantity 

 of the ashes of burnt bones." 



Fig. 1. — Erwin F. Smith of the United States Department of 

 Agriculture. 



Among the early chaff, however, there were some grains 

 of wheat. Thus Riedel in 1751 advised excision followed by 

 grafting wax for canker, and Robertson in 1821 said: "Sulfur 

 is the only specific remedy that can be named for the treat- 



