224 ON THE CORSICA N FIK. 



resinous fluid. As they always occur singly and in small num- 

 bers, they do not sensibly affect the technical qualities of the 

 timber, although the substance contained in them is of no mean 

 importance. These canals are to be found only in the bark and 

 in the so-called autumnal zone of the autumnal rings. As they 

 are connected with the medullary rays, the essential oil or fluid 

 is enabled to circulate throughout the whole tree; on coming in 

 ■contact with the atmosphere it becomes more or less hard and 

 brittle by a process of oxidation. As the Corsican fir gets older, 

 this fluid stores itself up in the inner wood, now inactive, and 

 forms an apparent heart, easily distinguishable, however, from 

 the true heartwood. 



The presence of resin makes the wood hard, limits the bounds 

 of elasticity, but renders it more tough or flexible ; it therefore 

 makes the wood more difficult to split ; but when a large supply 

 of resin is present it then becomes brittle. Eesinoiis timber 

 offers most resistance to the inroads of disease, since the woody 

 fibres are thus guarded against the influence of moisture and of 

 atmospheric oxygen, and is least exposed to the attacks of insects 

 that only find a too favourable breeding-place in timber already 

 in an unhealthy condition. 



A thin section of the wood will be found to have a silky gloss 

 ■on account of the medullary rays being very minute and close 

 together. 



In referring to the specific weight and techuical qualities of 

 the wood of the Corsican or Austrian fir, it must be observed 

 that the ^lues assigned can by no means remain constant; they 

 vary not only according to the strength of the soil over which 

 the tree has grown, and with the amount of moisture contained 

 . in the same, but also according to the exposure of the hill-sides 

 towards one or other of the points of the compass. A soil too 

 rich or too moist produces light and porous wood with little 

 resin ; northern slopes yield a larger quantity of timber but of 

 an inferior quality to that which is grown on hill sides with a 

 sunny southern aspect. 



A difference between the wood of conifers and that of other 

 forest trees is here worthy of note, since it, of course, immedi- 

 ately affects the timber of the Corsican fir. The wood of the 

 conifers is, as a rule, heavier and more durable the smaller the 

 annual rings are, while the reverse holds good of that of other 

 forest trees. Experiments have shewn that, no mattter how broad 

 the annual rings may be, the compact so-called " autumnal zone " 

 acquires in conifers, as a rule, dimensions not determined by the 

 breadth of the "spring zone;" in other words, when the annual 

 rings are broad the diameter of the compact zone is small, when 

 they are small it is large, in comparison to the diameter of the 

 whole year's ring. On the other hand, in such forest trees as 



