THE POTATO 181 



ually increase in size and become brown, this con- 

 dition being followed by the curling of the leaves. 

 If the under surface of a diseased leaf is examined 

 with a magnifying glass, the fruiting branches of 

 the fungus will be seen forming a delicate white 

 mold. 



"The spores of the fungus are exceedingly 

 numerous and minute, and are scattered by wind, 

 or by ground game and other animals running 

 amongst the plants. When it is stated that every 

 spore brought into contact with a damp potato 

 leaf is capable of starting a new centre of infection, 

 the rapid spread of the disease under favorable 

 conditions will be readily understood. The disease 

 develops and spreads with the greatest rapidity 

 during damp, warm weather, such as often occurs 

 in July. 



"Spores that fall to the ground are washed 

 through the soil by rain and may infect young 

 potatoes, especially those growing near the sur- 

 face. It is probable, too, that the mycelium of 

 the fungus passes down diseased stems into the 

 young potatoes. If the season be wet and warm 

 the mycelium present in the potato continues to 

 grow, soon causing brown spots to appear, and 

 ending in the rotting of the tuber. On the other 

 hand, if potatoes that are infected be kept dry, 

 the mycelium in their substance may remain 

 stationary until the following spring, when it may 

 commence growth and infect the new crop, after- 

 ward appearing in the fruiting condition on the 

 leaves. 



"Preventive and remedial measures suggested 

 are: 



" 1 . Potato disease is propagated and carried on 

 from season to season in the sets. It is therefore 



