1 6 PRACTICAL TREE REPAIR 



water. The great importance of the heartwood 

 lies in its resilient strength as a support to the 

 crown of the tree. It is just as dead in the tree 

 as it is when it is cut up into boards and built into 

 a house. It can be removed from the tree by man 

 or by fungous decay without the least injury to the 

 tree, provided the strength it represents is not 

 needed, or can be supplied in some other way. 



The bark is made up of cells produced from the 

 cambium or a sort of assistant cambium called the 

 phellogen. In rough-barked trees the bark is 

 added to from within in annual layers. The pres- 

 sure generated by this constant addition from with- 

 in, added to that caused by the annual increment of 

 the wood itself, causes the outer layers of the bark 

 to break in irregular fissures, and ultimately to 

 slough off in plates and flakes. In the smooth- 

 barked trees a different method is pursued. The 

 beech, for instance, has but very little corky bark, 

 most of the apparent bark being live " phloem " 

 tissue, which meets expansion by itself growing and 

 expanding, thus preventing the formation of fur- 

 rows in its surface. The sole purpose of the bark 

 is to protect the cambium and wood. 



It is in the cambium, as we have seen above, that 

 the digested sap from the leaves circulates about 

 the tree and passes down into the roots. Cambium 

 cannot live without some of this sap, and cannot 

 produce thrifty growth without a plentiful supply 



