APPLE DISEASES 147 
apples and other trees in close proximity are likely to become 
afflicted. The disease is recognized on cotton by a sudden 
wilting, usually during the latter part of June or early July, 
such symptoms being exhibited by isolated plants here and there 
in the field. 
Apples affected with Ozonium root-rot show a sudden wilting 
and death of the leaves; this is particularly characteristic of 
young trees. In case of old trees death is more gradual. In 
general affected trees have an abnormal, sickly appearance for 
a year or more prior to actual death. The causal fungus 
surrounds the tap root as well as the lateral roots; such 
roots die, decay, and thus cannot function, either in lending 
mechanical support to the tree or in furnishing the top with 
water and food. 
Cause. 
Numerous theories have been advanced by growers to explain 
the causal relationships of the Ozonium root-rot. But, as al- 
ready intimated, the fungus Ozonitwm omnivorum creates the 
disturbance. It lives and spreads in the soil and seems to have 
a decided preference for the Houston clay or black waxy soils 
of the Southwest. The fungus grows best where soil aération 
is the poorest. A high temperature and plenty of moisture are 
favorable to its development. Therefore the hot weather of 
the South favors it; and it flourishes where there is excessive 
water of irrigation, if other conditions are favorable. 
Once in the soil the fungus is washed about, and finally a root 
is encountered. The bark and woody tissues are penetrated, 
their cells being killed as the mycelium proceeds; ultimately 
decay is the result. After its work is complete, the mycelium 
breaks up into segments which are washed away to other roots 
of the apple or other plants. It may also spread by growing 
through the soil on decaying material, or may be carried by 
tools used in cultivation. No special fruiting bodies are 
known. 
