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-lice, 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 live, 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 
