TIM!?!-; II 7 



are the annual rings in the cross section of the wood, the 

 produce of successive seasons ; these trees are often spoken 

 of as exogenous or outward growing, their diameter 

 increasing yearly, in contrast to the palms, called inogenous, 

 and which, as a rule, grow only in length, their diameter 

 being the same at five years old as at fifty. 



Wood is composed of duramen or heartwood, and 

 alburnam or sapwood, and when dry consists approxi- 

 mately of 49 per cent, by weight of carbon, 6 per cent, of 

 hydrogen, 44 per cent, of oxygen, and 1 per cent, of ash, 

 which is fairly uniform for all series. The sapwood is the 

 external and youngest portion of the tree, and often a very 

 considerable proportion. It lies next the bark, and after a 

 course of years, sometimes many, as in the case of oaks, 

 sometimes few, as in the case of the firs, it becomes 

 hardened and ultimately forms the duramen. Sapwood is 

 generally of a white or light colour, almost invariably 

 lighter in colour than the heartwood, and is very con- 

 spicuous in the darker coloured woods, as for instance the 

 yellow sapwood of mahogany and similar coloured wood, 

 and the reddish brown heartwood or the yellow sap of 

 lignum vitae and the dark green heartwood. Sapwood 

 forms a much larger proportion of some trees than others, 

 but being on the outer circumference it always forms a 

 large proportion of the timber, and even in sound, hard 

 pine will be from 40 per cent, to 60 per cent, of the tree, 

 and in some cases much more. It is really imperfect wood, 

 whilst the duramen or heartwood is the perfect wood ; the 

 heartwood of the mature tree was the sapwood of its 

 earlier years. Young trees when cut down are almost all 

 sapwood, and practically useless as timber ; it is, however, 

 through the sapwood that the life-giving juices which 

 sustain the tree arise from the soil, and if the sapwood be 

 cut through, as is done when "girdling" teak, the tree 



