144 MANUAL OF TREE DISEASES 



Cause of Endothia canker. 



The canker of chestnut is caused by the perithecium-forming 

 fungus Endothia parasitica, formerly called Diaporthe parasitica. 

 The mycelium may grow parasitically in the bark, cambium 

 and sapwood of all parts of the chestnut tree above ground or 

 saprophytically on bark, twigs and dead parts of chestnut 

 and other trees. In the northern states new cankers may 

 originate at any time of the year from March to October. The 

 dissemination of the fungus to healthy trees or healthy parts 

 of the same tree is accomplished by many different agencies. 

 The spores or the mycelium itself may be carried by the wind, 

 water, birds, quadrupeds, insects and often by man. The 

 spores and mycelium live through the winter uninjured and 

 are ready for dissemination in the spring when many primary 

 infections are started. The agency most largely concerned in 

 the rapid spread of this fungus from tree to tree is the wind, 

 while water is important in washing the spores from a canker 

 in the top of a tree to other parts of the same tree and to others 

 close by. A few of the millions of spores produced on a single 

 canker find lodgment on the bark of other chestnut trees after 

 a shorter or longer journey from the place where they were 

 produced. Bringing the spores into contact with the healthy 

 bark is not all that is sufficient, however, for the spores must 

 find a wound of some kind to accomplish infection. The 

 spores germinate during periods of moist weather and the short 

 germ-tubes enter the soft tissue of the bark through the wound. 

 If there is no wound in the cork-layer, the germ-tubes of the 

 spores are unable to penetrate. An abundant growth of my- 

 celium rapidly develops from the germ-tube and in a few days 

 thin fan-like plates composed of thousands of threads of my- 

 celium, growing side by side, push out into the soft tissues of 

 the bark which lie between hard fibrous layers (Fig. 18). The 

 cells are killed a little in advance of the mycelium by certain 

 poisons which are excreted. Therefore, as these mycelial fans 



