INTRODUCTION 



The vital processes which constitute the physiology of plant 

 life are beyond the scope of this work : it deals solely with 

 their product — the wood, which while living is a tree, but being 

 dead is timber. The structure which has been described is 

 evident in whatever form the timber may be found, but, as the 

 conversion of the log into useful pieces entails the division of 

 the tree in many different ways, it requires a little more atten- 

 tion to follow it through its changes of appearance. 



As, then, a tree consists of concentric cones of wood, if it is 

 sawn into planks the outermost plank will be a curved flitch of 

 bark, with some sap-wood on its inner side. The next plank will 

 have sap-wood on each edge, and a strip of heart-wood down 

 the middle, which strip will increase in width, plank by plank, 

 until the centre of the tree is reached. Lines which mark off 

 cone from cone (that is, annual ring from annual ring), may seem 

 parallel at the lower end, but will join as loops; at the upper. 

 It is only when the section approaches the horizontal that the 

 annual rings approach the circular, so that oblique cuts show an 

 almost infinite variety of form. In fact, two planks are never 

 alike in every detail of figure except by accident. An in- 

 teresting experiment is to slice a hyacinth or other " tunicated " 

 bulb in various directions to see how great a variety of forms is 

 produced by the section of its many coats, and there is nothing 

 which can afford a better interpretation of the structure of the 

 annual rings of a tree. 



I have referred to the Autumn and Spring zones as though 

 all woods possessed them, and it will be found that the same 

 expressions are generally employed in the literature of Forestry. 

 They are, of course, only appropriate in connexion with those 

 species which grow in temperate climates, as the period of greatest 

 vigour in tropical trees is not necessarily that of Spring, while 

 it is possible that there is no resting period like our Winter. 

 Judging from the structure this state of things is by no means 

 unusual, and from British Guiana come a number of species, 

 conspicuous amongst which is the Greenheart (Fig. 99), now so 

 largely used for piles and wharf-timbers, which display no indi- 

 cation whatever of a regular alternation of seasons. 



In most works on Forestry much stress is laid upon the width 

 of the annual rings, and careful measurements have been made 

 to ascertain the average width, in order to supply data for 

 estimating the probable annual production of wood. As this 

 is the measure of profit the importance of these figures cannot 

 be overrated, but inasmuch as they have little, if any, value 

 for the purpose of identification, I have only mentioned them 

 by the way. The annual increase of the Rock Elm, which, 

 as its name implies, grows amidst barren rocks, is naturally 



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