CHAPTER XI 

 WOOD-ROTS : THE TREATMENT OF TREES 



Structure. 



For the purpose of this section a tree or shrub (excepting 

 coconut and other palms) may be regarded as a more or less inert 

 framework of wood, composing the root, stem, and branch systems, 

 over which is stretched in a thin layer the active living substance 

 of the tree. The woody tissue, once it is matured, contains 

 relatively few living elements, and is capable of no further 

 growth. The wood functions as mechanical support and for 

 the passage of the soil solution from the roots which absorb 

 it to the leaves which discharge its surplus water. In some 

 species only the outer layers of the stem (sapwood) are concerned 

 in conduction, the remainder, the heartwood, being quite lifeless, 

 in other species all the wood continues to function to some extent. 



Outside the wood lies what is popularly known as the bark, 

 which consists of (i) the inner living layers, the bast, and (2) the 

 outer dead layers of covk, the bark proper. An important 

 function of the bast is the transference of the food materials 

 elaborated in the leaves, including the supply of the necessary 

 nourishment to the roots. The bark is protective in its functions, 

 as will be noted later. Between the wood and the bast is an 

 extremely thin layer of delicate actively dividing tissue : the 

 cambium layer. From this the growth in thickness of all the 

 permanent parts of the tree proceeds. From its inner face 

 continuous new layers of wood are deposited on the old, and from 

 its outer face new layers are added to the bast. 



Increase in length of any woody organ takes place only by 

 additions to its outer end, and these are made at intervals by the 

 outgrowth of buds into new leafy shoots. 



Wood-rots. 



It will be readily understood, from what has been previously 

 said of resistance, that the wood, with its relatively few living 

 elements in the sapwood and none in the heartwood, will be sus- 

 ceptible to the attacks of fungi. There is in fact a very large 

 number of fungi which specialise in wood destruction, many of 

 them saprophytes, infesting dead wood with effects universally 

 familiar, others with various grades of ability to attack the wood 

 of living trees. 



When a tree is intact the wood is completely enclosed, first 

 by the outer bark, which is impervious to water, and even to air 

 except through the special breathing organs (lenticels), and is 



