98 ROTATION FOR QUALITATIVE EXPLOITABILITT. 



heart and sapwoods. Again large ■logs can be cut up into more 

 useful scantlings ; thus they may be first cut up into quarters before 

 undergoing further conversion, or they may be sawn up into broad 

 scantlings which are in great demand for certain purposes. This 

 advantage becomes most striking in the case of species valuable for 

 certain special characters, notably so in that of the oak, the ash &c. 

 To resume in a few words what precedes, we may say that the largest 

 logs are destined to supply the most important wants and this mor« 

 fully both as respects quantity and quality than smaller pieces, 



Theheartwood of trees' does not improve with age; on the con- 

 ^trary it deteriorates by gradually losing some portion of its com- 

 ponent elements, and even begins to decompose, as is proved by the 

 various alterations of colour which old wood undergoes. If it is a 

 desirable thing to obtain large trees, it would be no less undesirab'Ia 

 to let them deteriorate standing. Now experience shows that the 

 -deterioration of standing timber does not begin except with the 

 decay of the tree, so that instead of waiting until ihat stag'C super- 

 venes, we must fell all trees as soon as they are mature. 



This latter stage, which precedes tie beginning of decay, can 

 be recognised by a visible loss of vigour,; the annual shoots remain 

 very short, the foliage becomes spare and of a dull green. The stage 

 of decay on the other hand, shows itself by the loss of important 

 organs ; some of the principal branches in the top of the crown die, 

 and in consequence the foliage of the tree is entirely wanting in 

 places. For each species the mature tree and the tree in full decay 

 are recognised by special physical signs. The mature oak possesses 

 only a few scattered leaves which turn yellow early in autumn and 

 begin to fall from the top downwards ; entering the stage of decay, 

 it becomes stagheaded. The mature silver fir possesses a tabular 

 crown completely flattened at the top, and the lower branches are 

 but scantily furnished with leaves ; when decay sets in, the crown 

 loses its shape and, from having been circular, its outline becomes 

 irregular. Sometimes premature decay occurs. It is either acci- 

 dental and special to the tree affected, or general throughout a forest^ 

 When accidental, it may be due to a broken branch, for instance, or 

 to any other extraneous cause. To recognise it, it is necessary to 

 examine the crown, the bole and the butt-end, including the visible 

 spread of the principal roots. If the decay affects trees in a general 



