462 NATURE STUDY AND LIFE 



Mildews, or Moulds of the Garden. The moulds that attack 

 plants are commonly known as mildews, rusts, blights, or 

 smuts. The number of these minute parasitic fungi is 

 legion, and as a group they rank with destructive insects 

 in rendering the raising of flowers and fruits difficult and 

 interesting. We can introduce into the course only a 

 few of the more important, such as are most closely asso- 

 ciated with the children's garden studies. They may be 

 considered as types to indicate methods of study that can 

 be applied to many other kinds. The methods of uni- 

 versal application, for preventing fungous diseases of 

 plants, relate to intelligent cleanliness of garden and 

 premises (the burning of rubbish and dead leaves that 

 may harbor the spores) and to so planting and pruning 

 as to admit sunlight and air to every part of the plant. 

 For recent information about more special methods we 

 should send to our State Experiment Station for the 

 latest Spray-Calendar. 



The Black Knot, Ploivrightia nwrbosa. Request the children to 

 search their plum and cherry trees, bring in specimens, and report 

 the distribution and prevalence of this fungus in the neighborhood. 

 The summer crop of spores is produced in June. The knot at this 

 time is greenish brown and velvety. The winter spores are produced 

 in capsules in the black mass. From about December and for the 

 rest of the winter these capsules are perforated and the spores are 

 shaken out by every puff of wind, like pepper out of a pepper box. 

 The spores that happen to lodge behind a bud or in a crotch or 

 crevice send their mycelial threads into the living wood, where they 

 multiply greatly and thus cause the swelling or knot. Finally, they 

 send fruiting hyphas to the surface, and the life story is repeated. 

 A single knot is thus a menace to an orchard or neighborhood ; one 

 should never be permitted to develop spores, but should be cut off 

 and burned as soon as any swelling appears. 



