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fungus break through in the cracks of the bark. This is the condition 
existing at the base of most trees attacked, and only the most careful 
scrutiny will reveal the lesion. (See illustration material.) 
ETIOLOGY 
This canker disease of the chestnut is caused by the pyrenomycetous 
fungus, Endothia parasitica (Murrill) Andersons. It is a member of the 
order Sphaeriales. The conidial stage, considered by itself, falls in the 
genus Endothiella of the Fungi Imperfecti. 
Life-history. Primary and secondary life-cycles are not as sharply 
differentiated in E. parasitica as is usual with pyrenomycetous pathogenes. 
This is due to the lack of marked correlation between the periodicity of 
spore-form production in the fungus and seasonal periodicity. Cycles 
are initiated by ascospores or conidia at any time when moisture and 
temperature permit. Those initiated early in the spring are to be regarded 
as the primary cycles. ; 
The Primary Cycles may be initiated, as indicated above, by either of 
two kinds of inocula. 
Pathogenesis. 
(a) Ascospores are produced within perithecia developed in 
superficial strornata on the older portions of a canker or on dead twigs 
and bark. The production of ascospores is not limited to any specific 
time of year. It takes a certain time (depending on seasonal conditions) 
to develop perithecia after a new infection. If this period is interrupted 
by winter, development is simply arrested until spring. Therefore only 
those perithecia which were in a certain stage of development are mature 
in the early spring. 
In the material and photographs, NoTr :— 
9. The perithecial stromata, dark chocolate-brown in color. 
The surfaces of the mature stromata are covered with small projections or 
papillae, each with a small black dot at the apex. This is the ostiolum 
of a perithectum embedded in the stroma. (Illustration photograph 11.) 
DRAW. 
Crush a bit of this stroma and oBsSERVE:— 
10. The ascospores; two-celled, hyaline, eight in each ascus 
(photographs 34-37). DRaw. These ascospores are forcibly discharged 
by the bursting of the asci as they accumulate on top of the papillae after 
being crowded out through the ostiolum. 
If material is available study the violent discharge of the spores. With 
the hand-lens, oBSERVE-— 
; 11. The tiny points of light popping from the ostiola of the 
perithecia. 
Make a sKETCH to show ascospore-discharge. 
Hold clean dry slides at different heights above this material and 
determine the distance to which spores are shot in a vertical direction; 
also in a horizontal direction. From these slides, NOTE :— 
12. That the whole contents of the ascus is ejected at once. 
Ascospores germinate as soon as discharged, if they fall in water. DRAW 
a germinating ascospore showing the germtubes (Cornell Bul. 347 568). 
__ (b) Conidia are produced within subcortical or superficial 
pycnidia (illustration photograph 10a and photograph 12). Pycnidial 
