Effect of Soil Conditions 57 



diseases of foliage are present, such as those produced by 

 insects or fungi, the diagnosis is comparatively easy and 

 the remedy readily suggested ; but in the absence of such local 

 disturbances, when the e^•ident abnormahty of the foliage 

 is due to more remote causes, the difficulty is greater. As 

 long as fungus growth or insect depredations on bark, wood 

 and root, can be discovered as likeh' to have produced the 

 disturbance in the condition of the foliage, even a layman 

 may find the cause; but to diagnose the so-called physiolog- 

 ical diseases which are due either to permanent changes, or 

 to some unusual temporary conditions in the environment, 

 the ser\'ices of an expert may be required. 



Changes in the conditions to which the tree was originally 

 adapted may take place in the soil or in the light supply 

 (when neighbors are removed or are crow^ding), or they 

 may simply be in the weather conditions of the particular 

 season, or, in many cases, the combined conditions of soil 

 and season etfect the sickness. 



Indeed, whenever the conditions of nutrition are inter- 

 fered with, the foliage will soon give evidence of it. And 

 in this connection, the soil conditions, especially the mechan- 

 ical conditions which influence water and air supply, are 

 of the greatest importance, as these are the ones which can 

 be more or less controlled. 



Effect of Soil Conditions. It must not be overlooked that 

 a soil changes in its stucture and thereby in its capacity for 

 water conduction and aeration by the compacting of rain- 

 drops, by frost, and in many other ways, so that the same 

 soil Vv^hich was originally satisfactory to tree growth, may in 

 time become less so. Not only soils exposed directly to 

 rains, but also those under sod, or even under sidewalks, 

 become constantly more and more compacted, and hence a 

 gradual change in their permeability to Vv-ater and air takes 



