4 



is by robbing the tissues of their host plants of food that 

 the fungus plants produce their injuries. Upon the threads 

 of the fungus plants there are produced in various ways 

 little bodies called spores, which correspond to the seeds of 

 higher plants, ^'. e., they are the means of reproduction of 

 the fungus. The spores are usually produced in immense 

 numbers. When mature they are easily detached, and 

 being so light are readily distributed by the wind, just as 

 the seeds of many weeds are scattered. 



The spores under proper conditions of temperature and 

 moisture germinate, and if they chance to be upon a suita- 

 ble plant, develop into a fungus similar to the one which 

 produced them, and thus spread the disease. 



These diseases do not affect all plants indifferently, but 

 each plant has its own peculiar enemies. Certain conditions 

 of weather affect more or less their development, a warm, 

 moist season being especially favorable to them. Other 

 things being equal, thrifty plants are less liable to be 

 attacked than the opposite. 



It has long been known that the injuries of insects could 

 be largely prevented by applying to the affected plants 

 certain poisonous substances, such as hellebore, Paris green, 

 London purple, etc. These substances seem to have no 

 effect upon fungus diseases ; but others have been found 

 which have proved to be very effectual in their treatment. 

 Among these, the most valuable are copper carbonate and 

 copper sulphate, the latter being commonly known as blue 

 vitriol or blue stone. They are prepared in various ways, 

 and sprayed upon vines or trees, there coming in contact 

 with the fungus spores which are liable to be present, and 

 killing them. 



This treatment must be considered preventive rather 

 than curative, for in many cases after the fungus has gained 

 an entrance to the tissues of the host plant, it is out of reach 

 of the spray and will develop in spite of it. In the prepara- 

 tion of fungicides the following formulas are recommended : 



