FIG. 94 Peridermium harknessi, a destructive parasite on 

 various conifers in the United States, i, portion of the stem of 

 a seedling three years old, of Pinus ponderosa, showing the 

 aecidia of the Peridermium bursting through the bark ; 2, 

 appearance of portion of a stem of the same species of host, eight 

 years old, attacked by the fungus, the swollen portion being 

 thickly covered with aecidia that have burst through the bark ; 3, 

 section through fig. 2 : the shaded portion indicates the number of 

 annual rings of wood that have been stimulated to excessive 

 growth by the mycelium of the fungus. All the tigs, slightly 

 reduced. 



