89 
In the Secondary Cycles all the structures and phenomena of the 
primary cycles are exactly repeated. Secondary cycles differ in no way 
from the primary except in the time of year at which they are initiated. 
Pathological Histology. The mycelium of the fungus kills the cells 
of the bark, cambium, and sap-wood. The cells are killed in advance 
of the mycelium, presumably by excreted toxins. 
In the sections of cankers provided, OBSERVE :— 
30. The discoloration of the tissues affected. Make a diagram- 
matic DRAWING illustrating the enlargement of the canker. 
31. The septate and abundant mycelium. Often mycelial fans 
are formed in the bark. By stripping off the bark of a fresh canker, 
this is easily observed. (See demonstration microscopes for cross-sections 
of healthy and diseased twigs or see Phytopath. 4:191-200.) 
REPORT 
1. Bearing in mind the pertinent facts of the life-history of E. 
parasitica (Murr.) Andersons, enumerate and discuss the reasons why the 
Endothia disease is difficult to control. 
