190 Melanose and Stem-End Rot [388 



although organic deposits occur down to the frost line. 

 These deposits are lamelliform, and each appears to be con- 

 tinuous from its lowest point to the surface of the soil. 

 Whether they originated from the decay of roots that had 

 penetrated this layer while it contained more water than it 

 does now., or whether they were formed by slow seepage 

 from the surface, cannot be decided from the information at 

 hand. The occurrence of small landslides in which dry soil 

 was found above and below the layer in which the slipping 

 occurred, indicates., however, that water may move in a thin 

 sheet of soil and either form these deposits by carrying or- 

 ganic matter from the surface, or, finding them ready formed, 

 traverse them to the deeper portions. Since these layers are 

 rich in organic matter it is probable that their constituents 

 would cohere when frozen, which is not true of the dryer 

 soil about them. This may perhaps account for the state- 

 ments often made that in the winter or spring, frozen soil 

 may be encountered at the surface and also below it, in 

 sheets, at intervals. 



Whether due to this drying and being frozen in the dry 

 condition, or to other more obscure causes, the soil of this 

 dry layer is often flocculated to such a degree that it resem- 

 bles a mass of small clay pellets. Even after wetting this 

 flocculated soil retains its spherulate character. 



THE GEOGRAPHICAL DISTRIBUTION OF THE CITRUS 

 DISEASES, MELANOSE AND STEM-END ROT 



By H. S. FAWCETT 



A general survey of the citrus districts of the United 

 States and Cuba has shown that the distribution-areas of 

 some of the important fungus diseases are not coextensive 

 with the areas where the host is cultivated. This fact is 

 strikingly brought out by an examination of the distribu- 

 tion of some of the diseases that have been present in these 

 regions for a long time. 



