TIMBER 
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 Hes 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 vitse 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 
