158 STUDIES OF TREES 



ami limbs of trees, some attack the leaves, some the twigs 

 and others the roots. Some fungi grow on living wood 

 some on dead wood avi some on both. Those that attack 

 the living trees are the most dangerous from the stand- 

 point of disease. 



The chestnut disease: The disease which is threaten- 

 ing the destruction of all the chestnut trees in America 

 is a fungus which has, Avithin recent years, assumed such 

 vast proportions that it deserves special comment. The 

 fungus is known as Diaporthe parasitica (Murrill), and was 

 first observed in the vicinity of New York in 1905. At that 

 time only a few trees were known to have been killed by 

 this disease, but now the disease has advanced over the 

 whole chestnut area in the United States, reaching as far 

 south as Virginia and as far west as Buffalo. Fig. Ill 

 shows the result of the chestnut disease. 



The fungus attacks the cambium tissue underneath 

 the bark. It enters through a wound in the bark and 

 sends its fungous threads from the point of infection all 

 around the trunk until the latter is girdled and killed. 

 This may all happen within one season. It is not until 

 the tree has practicallx^ been destroyed that the disease 

 makes its appearance on the surface of the bark in the 

 form of brown patches studded with little pustules that 

 carry the spores. When once girdled, the tree is killed 

 above the point of infection and everything above dies, 

 while some of the twigs below may live until they are 

 attacked individually by the disease or until the trunk 

 below their origin is infected. 



All species of chestnut trees are subject to the disease. 

 The Japanese and Spanish varieties appear to be highly 

 resistant, but are not immune. Other species of trees 

 besides chestnuts are not subject to the disease. 



