Plants as Affected by Fungous Parasites. 175 



and pear, and the downy grape-vine mildew * may be 

 held in check by applying a fungicide (321 ) to the host 

 plant, to destroy the spores as they alight upon it. Vari- 

 ous compounds of copper and of sulfur are destructive 

 to the spores of fungi, and when properly applied, are 

 harmless to the plant. The copper compounds are more 

 generally satisfactory, since they have the greater ad- 

 hesive power. 





Fig. 78. A scab spot magni- 

 fled. (After Trelease). 



Fig. 77. Apple affected with scab 

 (the dai'k spots), Fusicladium de)t- 

 driticum. (After Scrlbner). 



Fig. 79. Section through a, 

 scab spot, highly magnified. The 

 egg-shaped parts at the right are 

 the spores. (After Trelease). 



329. The Bordeaux Mixture, which consists of a com- 

 pound of copper sulfate (324) and lime, is now extensively 

 used to prevent many fungous diseases of this class. A 

 standard formula for the Bordeaux mixture is : 



Dissohe 6 pounds of copper sulfate in 4 gallons of hot 

 water ; in another vessel slack 4 pounds of fresh quick- 

 lime in 4 gallons of (hot or cold) water. When both are 

 cool, pour the contents of the two vessels together and 



* Peroiiospora viticola. 



