78 HORTICULTURE LECT. v 



swim in the moisture, dew, or rain, on potato leaves. 

 They enter these through the pores, germinate, destroy 

 the tissues, and set up the disease, which spreads, 

 and has often ruined the crops. The fungus also 

 produces what are known as resting spores. These, 

 after much patient watching and waiting, were dis- 

 covered under the microscope by Mr. Worthington G. 

 Smith in 1875. 



These may be called the eggs of the potato dis- 

 ease. How long they retain their vitality is not 

 known. They wait for favourable conditions, then 

 become active, and carry out their destructive work. 



By placing these spores on the leaves of potatoes, 

 and on slices of the tubers, they grew, as seeds grow 

 under favourable conditions, and in that way the 

 potato disease was cultivated at will. For this im- 

 portant discovery a gold medal was granted to Mr. 

 Smith by the Royal Horticultural Society. He says 

 the potato disease spores abound in old moist potato 

 refuse in the course of decay, as in heaps with 

 manure. It is prudent then to dry and burn all the 

 potato tops possible, and so consume the eggs or 

 spores of the murrain. 



Other methods of preventing the potato disease 

 are good drainage, deep culture, and wide planting, 

 so as to produce stout plants with hard stems and 

 thick leaves, coupled with a dressing of sulphate of 

 copper and lime. This is applied both in water and 

 as powder. It has been of service on the Continent 

 against fungoid growths, and has been tried in many 

 places in England, in some instances with marked 

 success, rows to which it was applied being almost 

 free from the disease, while others not dressed were 

 a mass of blackness and decay. It is good also 

 against mildew on various other crops. 



In dealing with garden enemies, prevention is a 



