52 Diagnosing of Diseases 



injuries to the cambium and young wood, caused by insects 

 or other agencies, and the robbery by sucking insects like 

 the scale and bark-hce, affect the feeding processes of the 

 tree and may be the reason for the abnormal condition of 

 the foliage. 



If only certain portions of the foliage show abnormality, 

 it is almost certain that a localized cause will be found such 

 as a colony of insects, a partial destruction of food-conduct- 

 ing tissue, a particular root injury. If, on the other hand, 

 the whole crown is affected, the cause must be more general 

 and may be found in general conditions of nutrition. Then 

 it becomes necessary to examine the soil, to see whether in 

 any way conjectures as to the conditions at the root may 

 be formed, accounting for the indications in the crown. 



Here, in the root region, matters become more compli- 

 cated because hidden from direct observation, and yet here 

 lies probably the most fertile source of trouble. 



As so often in an old man head and feet become feeble 

 simultaneously, so in the tree, when the top gives out, there 

 is usually something wrong at the root, and that means 

 generally at the very extremities, — the root-tips. The dis- 

 tance from root-tip to branch-tip, from pump and power 

 plant to feeding extremities, increasing continuously, makes 

 naturally the life processes more and more difficult to per- 

 form at the extremities, and if any other cause of discomfort 

 is added, the result may be fatal. 



As on the leaves and bole, so on the roots, there are 

 predatory insects and fungi active and the roots are liable to 

 mechanical injuries with the same results. But, in addi- 

 tion, there are essential conditions in the soil, the medium 

 in which the roots hve, which can change to a much greater 

 extent than can those of the air, the medium of the upper 

 portions of the tree. As we have already seen, these changes 



