24 DISEASES OF DECIDUOUS FOREST TREES. 



The fungus usually gains entrance through some wound in the root 

 system, although it has been maintained that it can penetrate the 

 bark of uninjured trees. The young mycelium grows into the 

 cambium layer, attacks the living cells, and finally completely encir- 

 cles the base of the trunk of an affected tree. As the fungus continues 

 to develop, masses of the mycelium form rhizomorph strands. The 

 ultimate effect of the presence of the fungus is to kill the living layers 

 of the tree near the ground line, causing a drying of the top and the 

 ultimate death of the entire tree. 



The fungus continues to live in the dead root system and in the base 

 of the trunk of the tree for a number of years, and the rhizomorphs 

 are able to continue their growth from root to root for some years 

 after the trees have died. It is this faculty which makes this fungus 

 an exceptionally dangerous one, because it is thereby enabled to 

 spread from tree to tree through the soil with great readiness. The 

 writers' observations show that the dead pieces of roots left in newly 

 cleared forest land are sources of infection for the roots of fruit trees 

 when planted on such land a few years later. 



The second fungus, which affects trees very much as does the honey 

 mushroom, is a root fungus ( TlielepJiora galactina Fr.) (82) which has 

 so far been found only on various species of oak, particularly the 

 black oak. It has been found to occur commonly in various parts of 

 the Ozark Mountains in southwestern Missouri, western Arkansas, 

 and eastern Indian Territory. The long white strands of this fungus 

 penetrate the bark of oak trees until they reach the living tissues. 

 The fungus generally attacks the younger trees, and when the soil 

 conditions are favorable for its development, considerable areas of 

 oak forest may be killed as a result of its activity. It is one of those 

 forms which cross from oaks to fruit trees when planted on newly 

 cleared land. 



SLIME-FLUX DISEASES. 



A class of diseases known as slime-flux diseases should be referred 

 to here, because they are frequently found on many of the deciduous 

 trees. The slime-flux diseases are common in this country on the yellow 

 birch (Betula lutea Michx. f.), elm ( Ulmus americana L.), dogwood 

 (Cornus florida L.), apple (Pyrus malus L.), and maples {Acer spp.). 

 They are characterized by the appearance of various colored, slimy 

 masses with a decidedly acid odor, which start at or near wounds 

 caused by different agencies (23, 102). They make their appearance 

 usually early in the spring when the sap, containing more or less 

 sugar, flows from the wounds mentioned. In this sap a number of 

 forms of algae, bacteria, and fungi, usually associated with certain 

 low animal forms, flourish extensively. The fermentive processes 

 set up by one or all of these forms kill the underlying bark and cam- 



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