492 CITRUS FRUITS AND THEIR CULTURE. 



root and branch. It is probable that the causative agent 

 moves through the soil in the ground water. This may ex- 

 plain the apparently contagious nature of the disease. 

 Nevertheless, the trees should be destroyed as already sug- 

 gested as the decaying roots in the soil may tend to increase 

 the disease. If the disease is ever successfully combated, 

 it will probably have to come through the application of 

 some chemical substance to the soil. 



