322 DISEASES OF ECONOMIC PLANTS 



is harvested cannot be prevented by such means with- 

 out danger to the seed, but can be prevented by the 

 use of clean, uninfected seed. Corn, being susceptible 

 at all ages of its growth, cannot be protected by seed 

 treatment. 



Owing to their great damage and conspicuousness, smuts 

 have attracted attention from very early times, and many 

 references to them are found in ancient writings. Prob- 

 ably not until 1791, however, was their true nature as 

 vegetable parasites recognized. Many were the means 

 that were suggested for the prevention of these pests: 

 placing laurel branches in the field, change of seed, avoid- 

 ance of manures, thorough screening, soaking in brine, etc. 



Preventive treatments. — The only one of the early 

 treatments that has proved its value and remained in 

 common use is that of soaking the seed in copper sulphate 

 (bluestone), first tried byTessierin 1789, after he, in 1786, 

 and Young, in 1787, had tested numerous chemicals. His 

 test was without results, since during that season neither 

 treated nor untreated wheat was smutted. Prevost of 

 France in 1807 was the first to publish an account of the 

 successful use of bluestone for wheat smut. He recom- 

 mended a solution of about 6 per cent strength, and the 

 remedy was, and is still, widely used. Solutions varying in 

 strength have been employed, one half per cent being most 

 highly recommended. In 1873 Dreisch improved the blue- 

 stone treatment by using limewater to follow the blue- 

 stone; thus, to a large extent, diminishing the amount of 

 seed killed by the treatment. 



Jensen, a Dane, in 1887 and 1888 reported excellent 

 results with oat, barley, and wheat smuts from dipping 



