THE MONTHLY BULLETIN, 277 



patience and get pulled out. Two or three years or more may pass before 

 the disease spreads to the next tree. It is thus seen that the rate of 

 spread is slow, but we have maps of spots in citrus orchards fifteen 

 years old where 25 to 30 trees have been lost. In some cases practically 

 whole orchards have been swept over. Some have not been replanted. 

 Others have been replanted, part of the replants living and others dying, 

 so that the result is very discouraging. After the disease has become 

 well established occasional new centers of infection appear. It is 

 believed that probably such new infections arise from a diseased root 

 being carried along, and, before it dries, plowed under near a healthy 

 root. I have picked up from the moist cover-crop a piece of diseased 

 root which had fallen from the cart in which a dead tree was being 

 hauled from the orchard. If this root had been plowed under so as to 

 come near a healthy root the fungus would almost certainly have grown 

 over into the healthy root and in a few j-ears another tree would have 

 died and a new center of infection Avould have been established. 



Toadstools or mushrooms appear during early winter about most of 

 the sick and dead trees. These toadstools may continue to come up on 

 some stumps for at least five years. They are light tan color and are 

 found in large clumps. They arise directly from the diseased roots and 

 are the fruiting bodies of the fungus. White spores are found on them 

 in immense numbers, but probably these spores do not cause new infec- 

 tions in living trees, altliough we have repeatedly grown them artificially. 

 They might easih' infect a decaying stump. 



If we examine carefully a root newly killed by this fungus we see that 

 its bark is somewhat puffed and when cut into is soft and moist. By 

 care we can sejiarate it into layers exposing white plaques of fungus, 

 which are soft, felty, and tend to radiate out in fan-shaped bodies. The 

 appearance will vary somewhat according to the kind of tree. The 

 odor is a sharp, sweet mushroom odor and not putrid or sour. Precisely 

 such bodies are found in artificial cultures. Sometimes the bark is 

 cracked and fungus bodies pushed out into prominent ridges which are 

 black on the surface but white below. Roots which have been attacked 

 for some time will be found to have the wood with a white decay work- 

 ing in from the surface. After a time the wood becomes very soft and 

 moist and finally almost completely disappears. 



Dark brown to black shining root-like structures coming out of the 

 diseased bark and running along its surface are often found. These 

 are the rhizomorphs ; they resemble roots but have a different structure, 

 the center being composed of soft, white fibers. They give the fungus 

 the power to go several inches from one root to another. When the 

 tip of the rhizomorph comes to a healthy root the very small micro- 

 scopic threads of which it is composed seem to loosen like the cut end 

 of a rope and the individual threads penetrate into the bark and start 

 a new infection. 



Treatment for Oak Fungus. 



Prevention. It is often recommended to take great expense to get 

 out all roots from new land before planting. Evidently, the fewer roots 

 left in the soil the less chance there will be of infection. However, it 

 is not within the limits of practicability to get out all roots from wooded 

 land. A good practice would be to clear the land, cultivate thoroughly, 



